You searched for subject:(quantum phase transition).
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1.
Hollen, Shawna M.
Cooper Pair Localization in Thin Films near the
Superconductor-Insulator Transition.
Degree: PhD, Physics, 2013, Brown University
URL: https://repository.library.brown.edu/studio/item/bdr:320462/ 
► The superconductor-insulator transition (SIT) is a well-known phenomenon that is observed in many types of superconducting systems, including elemental films and high Tc superconductors. Ultrathin…
(more)
▼ The superconductor-insulator
transition (SIT) is a
well-known phenomenon that is observed in many types of
superconducting systems, including elemental films and high Tc
superconductors. Ultrathin films provide a versatile platform from
which to study this ubiquitous, and possibly universal,
transition.
Two different theoretical approaches have been made to describe the
SIT in thin films. The first predicts that Cooper pairs (CPs) exist
in the insulating
phase, and the second proposes that the
transition is driven by pair-breaking, yielding an insulator of
localized single electrons.
Recent experiments showing the existence of an insulating
phase of localized CPs have provided significant support for the
first mechanism. This CP insulating (CPI)
phase exhibits dramatic
transport features including a giant magnetoresistance (MR) peak.
Previous work in the Valles lab found such a
phase in ultrathin
amorphous Bi films quench-condensed onto a substrate with a
nanohoneycomb (NHC) hole array. The local Cooper pairing
correlations of the CPI
phase were evident from Little-Parks-like
MR oscillations due to the hole array.
This thesis describes investigations of the mechanism for CP
localization and the emergence of the CPI
phase in NHC films. There
are three main results. First, the CPI
phase appears to be induced
in NHC films by the undulating surface of the substrate, which
produces regular spatial variations in thickness that give rise to
nanoscale CP islands. Second, the giant positive MR characteristic
of the CPI
phase emerges with increasing film thickness
simultaneously with the MR oscillation signal, associated with
local CP
phase coherence. The insulating phases of the thinnest
films and films in magnetic fields just beyond the MR peak likely
consist of CPs totally localized to their islands. Third, amorphous
holey films of uniform thickness do not exhibit a CPI
phase. These
films go from superconductors directly to fermionic insulators with
decreasing thickness. These results lend further insight to the
nature of the CPI
phase and also require at least two classes of
SITs: one that can describe the presence of a CPI
phase and one
that can describe a
transition from a superconductor to a fermionic
insulator.
Advisors/Committee Members: Valles, James, Jr. (Director), Mitrovic, Vesna (Reader), Feldman, Dmitri (Reader).
Subjects/Keywords: quantum phase transition
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APA (6th Edition):
Hollen, S. M. (2013). Cooper Pair Localization in Thin Films near the
Superconductor-Insulator Transition. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:320462/
Chicago Manual of Style (16th Edition):
Hollen, Shawna M. “Cooper Pair Localization in Thin Films near the
Superconductor-Insulator Transition.” 2013. Doctoral Dissertation, Brown University. Accessed January 26, 2021.
https://repository.library.brown.edu/studio/item/bdr:320462/.
MLA Handbook (7th Edition):
Hollen, Shawna M. “Cooper Pair Localization in Thin Films near the
Superconductor-Insulator Transition.” 2013. Web. 26 Jan 2021.
Vancouver:
Hollen SM. Cooper Pair Localization in Thin Films near the
Superconductor-Insulator Transition. [Internet] [Doctoral dissertation]. Brown University; 2013. [cited 2021 Jan 26].
Available from: https://repository.library.brown.edu/studio/item/bdr:320462/.
Council of Science Editors:
Hollen SM. Cooper Pair Localization in Thin Films near the
Superconductor-Insulator Transition. [Doctoral Dissertation]. Brown University; 2013. Available from: https://repository.library.brown.edu/studio/item/bdr:320462/
Penn State University
2.
Yu, Jiabin.
Symmetry and Topology in Quantum Matter.
Degree: 2020, Penn State University
URL: https://submit-etda.libraries.psu.edu/catalog/17871jky5062
► Quantum states of matter at zero temperature are called quantum phases, which are characterized by their symmetries and topology. If two quantum phases cannot be…
(more)
▼ Quantum states of matter at zero temperature are called
quantum phases, which are characterized by their symmetries and topology. If two
quantum phases cannot be related by symmetry-preserving continuous transformations, they are defined to be topologically distinct. The zero-temperature transitions among
quantum phases are
quantum phase transitions.
Quantum phase transitions that happen among topologically distinct phases are called topological
quantum phase transitions. The study of topological
quantum phases and topological
quantum phase transitions is a central topic in condensed matter physics.
My research on
quantum phases has been focused on the theoretical study of topologically nontrivial
quantum phases in the crystals governed by non-interacting Hamiltonians, including topological insulator phases, topological semimetal phases, topological superconductor phases, and so on. First, we proposed a sufficient criterion that can efficiently determine whether a three-dimensional crystal is a topological semimetal or not, based on the compatibility of different expressions for a special topological invariant, the quantized bulk average value of the effective axion field. Second, we predicted the existence of various topological insulator phases and topological semimetal phases in half-Heusler materials. Third, we proposed the magnetic-resonance-induced current as a feasible experimental probe of a special kind of topological insulators, called the axion insulators. Fourth, we proposed a new pairing mixing mechanism, the singlet-quintet mixing, for superconductors with spin-3/2 fermions, demonstrated the topological superconductor
phase induced by it, and studied various properties of it, including spin-susceptibility, upper critical field, stability against the disorder, and surface Majorana flat bands.
Besides the topological
quantum phases, I have also worked on
quantum phase transitions. First, we constructed the first theoretical model for the emergent supersymmetry at a discontinuous
quantum phase transition and proposed to realize it on the surface of a topological superconductor. Second, we proposed the discontinuous change of piezoelectricity as a probe of two-dimensional topological
quantum phase transitions between insulating phases, through a systematic study of all the relevant gap closing cases. In this dissertation, I first briefly introduce the basic concepts in the field of topological
quantum phases and topological
quantum phase transitions with a focus on the crystals governed by noninteracting Hamiltonians. Then, I review in detail all my first-authored research works mentioned above. My other research works are briefly mentioned.
Advisors/Committee Members: Chaoxing Liu, Dissertation Advisor/Co-Advisor, Chaoxing Liu, Committee Chair/Co-Chair, Radu Roiban, Committee Member, Marcos Antonio Rigol, Committee Member, Venkatraman Gopalan, Outside Member, Nitin Samarth, Program Head/Chair.
Subjects/Keywords: Topology; Symmetry; Quantum Phase; Quantum Phase Transition; Noninteracting Crystal
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APA (6th Edition):
Yu, J. (2020). Symmetry and Topology in Quantum Matter. (Thesis). Penn State University. Retrieved from https://submit-etda.libraries.psu.edu/catalog/17871jky5062
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Yu, Jiabin. “Symmetry and Topology in Quantum Matter.” 2020. Thesis, Penn State University. Accessed January 26, 2021.
https://submit-etda.libraries.psu.edu/catalog/17871jky5062.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Yu, Jiabin. “Symmetry and Topology in Quantum Matter.” 2020. Web. 26 Jan 2021.
Vancouver:
Yu J. Symmetry and Topology in Quantum Matter. [Internet] [Thesis]. Penn State University; 2020. [cited 2021 Jan 26].
Available from: https://submit-etda.libraries.psu.edu/catalog/17871jky5062.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Yu J. Symmetry and Topology in Quantum Matter. [Thesis]. Penn State University; 2020. Available from: https://submit-etda.libraries.psu.edu/catalog/17871jky5062
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
3.
Das, Nabyendu.
Some aspects of quantum phase transition in incipient
ferroelectrics; -.
Degree: Physical Science, 2011, INFLIBNET
URL: http://shodhganga.inflibnet.ac.in/handle/10603/4723
None
Bibilography p.72-75
Advisors/Committee Members: Mishra, S G.Subjects/Keywords: quantum phase transition
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APA (6th Edition):
Das, N. (2011). Some aspects of quantum phase transition in incipient
ferroelectrics; -. (Thesis). INFLIBNET. Retrieved from http://shodhganga.inflibnet.ac.in/handle/10603/4723
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Das, Nabyendu. “Some aspects of quantum phase transition in incipient
ferroelectrics; -.” 2011. Thesis, INFLIBNET. Accessed January 26, 2021.
http://shodhganga.inflibnet.ac.in/handle/10603/4723.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Das, Nabyendu. “Some aspects of quantum phase transition in incipient
ferroelectrics; -.” 2011. Web. 26 Jan 2021.
Vancouver:
Das N. Some aspects of quantum phase transition in incipient
ferroelectrics; -. [Internet] [Thesis]. INFLIBNET; 2011. [cited 2021 Jan 26].
Available from: http://shodhganga.inflibnet.ac.in/handle/10603/4723.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Das N. Some aspects of quantum phase transition in incipient
ferroelectrics; -. [Thesis]. INFLIBNET; 2011. Available from: http://shodhganga.inflibnet.ac.in/handle/10603/4723
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
University of Minnesota
4.
Wang, Yuting.
Finite Size Scaling Around One Dimensional Topological Quantum Phase Transitions.
Degree: PhD, Physics, 2020, University of Minnesota
URL: http://hdl.handle.net/11299/215110
► The critical point of a topological phase transition is described by a conformal field theory. We first investigate the finite-size scaling away from criticality of…
(more)
▼ The critical point of a topological phase transition is described by a conformal field theory. We first investigate the finite-size scaling away from criticality of the ground state energy and find a scaling function, which discriminates between phases with different topological indexes. This function appears to be universal for all five Altland-Zirnbauer symmetry classes with non-trivial topology in one spatial dimension. We obtain an analytic form of the scaling function and compare it with numerical results. Then we verify the universality of the scaling function for the topological transition between dimerized and Haldane phases in bilinear-biquadratic spin-1 chain. To this end we perform high-accuracy variational matrix product state simulations. We show that the scaling function, expressed in terms of L/ξ, where L is the chain length and ξ is the correlation length, coincides with that of three species of non-interacting massive Majorana fermions. The latter is known to be a proper description of the conformal critical theory with central charge c=3/2. We have shown that it still holds away from the conformal point, including the finite size corrections. Finally we consider scaling of the entanglement entropy across a topological quantum phase transition for the Kitaev chain model. The change of the topology manifests itself in a sub-leading term, which scales as L-1/α with the size of the subsystem L, here α is the Rényi index. This term reveals the scaling function h_α(L/ξ), where ξ is the correlation length, which is sensitive to the topological index. The scaling function h_α(L/ξ) is independent of model parameters, suggesting some degree of its universality.
Subjects/Keywords: entanglement; finite size; quantum phase transition; topological
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APA (6th Edition):
Wang, Y. (2020). Finite Size Scaling Around One Dimensional Topological Quantum Phase Transitions. (Doctoral Dissertation). University of Minnesota. Retrieved from http://hdl.handle.net/11299/215110
Chicago Manual of Style (16th Edition):
Wang, Yuting. “Finite Size Scaling Around One Dimensional Topological Quantum Phase Transitions.” 2020. Doctoral Dissertation, University of Minnesota. Accessed January 26, 2021.
http://hdl.handle.net/11299/215110.
MLA Handbook (7th Edition):
Wang, Yuting. “Finite Size Scaling Around One Dimensional Topological Quantum Phase Transitions.” 2020. Web. 26 Jan 2021.
Vancouver:
Wang Y. Finite Size Scaling Around One Dimensional Topological Quantum Phase Transitions. [Internet] [Doctoral dissertation]. University of Minnesota; 2020. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/11299/215110.
Council of Science Editors:
Wang Y. Finite Size Scaling Around One Dimensional Topological Quantum Phase Transitions. [Doctoral Dissertation]. University of Minnesota; 2020. Available from: http://hdl.handle.net/11299/215110
University of Minnesota
5.
Lin, Yen-Hsiang.
Electrical transport properties of ultrathin amorphous bismuth films near the superconductor-insulator transition.
Degree: PhD, Physics, 2011, University of Minnesota
URL: http://purl.umn.edu/115916
► A combination of thickness- and perpendicular magnetic field-tuning of SI transitions has been performed on quench-deposited homogeneous a-Bi thin films with a 14.67 Angstrom a-Sb…
(more)
▼ A combination of thickness- and perpendicular magnetic field-tuning of SI transitions has been performed on quench-deposited homogeneous a-Bi thin films with a 14.67 Angstrom a-Sb underlayer. Transport properties, including measurements of resistance and of I-V characteristics have been studied in both the insulating and superconducting regimes. In the insulating regime, the resistance exhibits an Arrhenius type of conduction and the magnetoresistance (MR) exhibits a peak in perpendicular magnetic field. Furthermore, a possible quantum phase transition is found in the insulating regime. Presumably this transition is between the Bose and Fermi insulators discussed in the literature. The I-V characteristics exhibit strong non-linearities in the insulating regime at low temperatures. These non-linear curves can be well described by a heating model involving the decoupling of the electronic and phononic degrees of freedom at low temperatures. On the conductive or superconducting side of the transition, the transport properties are found to be remarkably similar to those of an overdamped random Josephson junction array, and vortex dynamics dominates the conductive behavior in both zero and non-zero magnetic fields. These observations suggest that isolated superconducting islands or localized Cooper pairs exist in both the insulating and conductive regimes. An AFM scan of the last film in the sequence has revealed that this series of films although continuous, has thickness variations on a mesoscopic length scale. Therefore, it is not surprising that there may be superconducting islands. The AFM scan also suggests that some of the thick, nominal granular films grown by quench condensed deposition are directly connected with large thickness variations. These insulating granular films also exhibit an Arrhenius type conduction at low temperatures, which reveals the existence of a hard gap in the electronic density of states, which is consistent with the theory of Feigel'man et al.. However, the activation energy of the Arrhenius type conduction found in the thickness tuning homogeneous a-Bi films doesn't follow this model. Therefore, the model may not completely explain the hard gap.
Subjects/Keywords: Disorder superconductor; Quantum phase transition; Superconuctor-Insulator transition; Physics
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APA ·
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APA (6th Edition):
Lin, Y. (2011). Electrical transport properties of ultrathin amorphous bismuth films near the superconductor-insulator transition. (Doctoral Dissertation). University of Minnesota. Retrieved from http://purl.umn.edu/115916
Chicago Manual of Style (16th Edition):
Lin, Yen-Hsiang. “Electrical transport properties of ultrathin amorphous bismuth films near the superconductor-insulator transition.” 2011. Doctoral Dissertation, University of Minnesota. Accessed January 26, 2021.
http://purl.umn.edu/115916.
MLA Handbook (7th Edition):
Lin, Yen-Hsiang. “Electrical transport properties of ultrathin amorphous bismuth films near the superconductor-insulator transition.” 2011. Web. 26 Jan 2021.
Vancouver:
Lin Y. Electrical transport properties of ultrathin amorphous bismuth films near the superconductor-insulator transition. [Internet] [Doctoral dissertation]. University of Minnesota; 2011. [cited 2021 Jan 26].
Available from: http://purl.umn.edu/115916.
Council of Science Editors:
Lin Y. Electrical transport properties of ultrathin amorphous bismuth films near the superconductor-insulator transition. [Doctoral Dissertation]. University of Minnesota; 2011. Available from: http://purl.umn.edu/115916
University of Southern California
6.
Jacobson, Noah Tobias.
Fidelity: A quantum information-theoretic approach to
problems in condensed matter physics and quantum chaos.
Degree: PhD, Physics, 2011, University of Southern California
URL: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll127/id/640834/rec/2806
► In this dissertation, we address several problems in condensed matter physics, statistical mechanics, and quantum chaos from the perspective of the quantum information-theoretic notion of…
(more)
▼ In this dissertation, we address several problems in
condensed matter physics, statistical mechanics, and
quantum chaos
from the perspective of the
quantum information-theoretic notion of
state distinguishability, as measured though evaluation of the
appropriate fidelity measure. ❧ We find that the fidelity
susceptibility, a measure for the response of the fidelity to
infinitesimal changes of the Hamiltonian parameters, serves as a
useful tool for studying the effects of disorder on
quantum phase
transitions. We study in detail the
phase diagram of the well-known
one-dimensional random
quantum XY chain. Through an analysis of the
fidelity susceptibility’s finite-size scaling and statistics for
this model, we find that the fidelity approach reflects large
variation between average and typical behavior, may detect the
presence of Griffiths phases, and indicates the modifications to
the
phase diagram due to disorder. ❧ For this same model, though
without disorder, we evaluate the dynamics following a sudden
Hamiltonian quench using the Loschmidt echo, a form of the fidelity
that compares the initial state with the time-evolved state.
Through a central limit theorem-type argument we find that the
long-time statistics of the Loschmidt echo takes one of two
universal forms, even at finite temperature, depending on the
system’s proximity to the
quantum critical lines. ❧ Finally, for a
canonical model exhibiting
quantum chaos, the hydrogen atom in a
uniform external magnetic field, we evaluate the operator fidelity
susceptibility (OFS) between unitary operators generating the
dynamics. We find that the part of the OFS which corresponds to the
variation of the Hamiltonian eigenvectors serves to indicate the
transition from the regular perturbative and n-mixing regimes to
the
quantum chaotic regime.
Advisors/Committee Members: Zanardi, Paolo (Committee Chair), Haas, Stephan (Committee Member), Lidar, Daniel (Committee Member), Brun, Todd A. (Committee Member), Jonckheere, Edmond A. (Committee Member).
Subjects/Keywords: fidelity; quantum phase transition; quantum chaos; Loschmidt echo; disorder; equilibration
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APA (6th Edition):
Jacobson, N. T. (2011). Fidelity: A quantum information-theoretic approach to
problems in condensed matter physics and quantum chaos. (Doctoral Dissertation). University of Southern California. Retrieved from http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll127/id/640834/rec/2806
Chicago Manual of Style (16th Edition):
Jacobson, Noah Tobias. “Fidelity: A quantum information-theoretic approach to
problems in condensed matter physics and quantum chaos.” 2011. Doctoral Dissertation, University of Southern California. Accessed January 26, 2021.
http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll127/id/640834/rec/2806.
MLA Handbook (7th Edition):
Jacobson, Noah Tobias. “Fidelity: A quantum information-theoretic approach to
problems in condensed matter physics and quantum chaos.” 2011. Web. 26 Jan 2021.
Vancouver:
Jacobson NT. Fidelity: A quantum information-theoretic approach to
problems in condensed matter physics and quantum chaos. [Internet] [Doctoral dissertation]. University of Southern California; 2011. [cited 2021 Jan 26].
Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll127/id/640834/rec/2806.
Council of Science Editors:
Jacobson NT. Fidelity: A quantum information-theoretic approach to
problems in condensed matter physics and quantum chaos. [Doctoral Dissertation]. University of Southern California; 2011. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll127/id/640834/rec/2806
Rice University
7.
Svanidze, Eteri.
Search, Discovery, Synthesis and Characterization of Itinerant Magnets Composed of Non-magnetic Constituents.
Degree: PhD, Natural Sciences, 2015, Rice University
URL: http://hdl.handle.net/1911/88169
► The origin of magnetism in metals has been traditionally discussed in two diametrically opposite limits: itinerant and local. Itinerant magnetism, caused by conduction electrons, has…
(more)
▼ The origin of magnetism in metals has been traditionally discussed in two diametrically opposite limits: itinerant and local. Itinerant magnetism, caused by conduction electrons, has been of interest due to intriguing phenomena that frequently accompany it: heavy fermion behavior, coexistence of superconductivity and magnetism, metamagnetic transitions, spin- and cluster-glass behavior, multisublattice magnetism, non-Fermi liquid behavior, and
quantum criticality. Surprisingly, while many systems exhibit both local and itinerant magnetism, only two are known to contain no local moment ions: Sc3In and ZrZn2. Doping experiments on Sc3In were used to investigate the effects of both magnetic (Er) and non-magnetic (Lu) substitutions within the itinerant matrix. While the former induces a cluster-glass state, the latter drives the system through a
quantum phase transition. A novel Arrott-Noakes scaling indicates that Sc3In cannot be described by the mean-field theory, contrary to what has been seen in ZrZn2. This indicates that ZrZn2 and Sc3In are drastically different, which is likely associated with the dimensionality of spin fluctuations. Given these disparities between two seemingly analogues systems, more itinerant compounds containing non-magnetic elements are needed. While the Stoner criterion for band ferromagnetism calls for high density of states at the Fermi level together with strong electron correlations, more conditions are likely at play. A systematic search among 3d systems resulted in the discovery of the first itinerant antiferromagnet composed of non-magnetic elements TiAu. The spin density wave antiferromagnetic ordering separates this compound from the previously reported ferromagnetic ones. Furthermore, perturbation of TiAu lattice with doping resulted in an antiferromagnetic
quantum critical point, which can provide insights on the validity of the self-consistent renormalization theory of spin fluctuations in itinerant magnets.
Advisors/Committee Members: Morosan, Emilia (advisor), Kono, Junichiro (committee member), Du, Rui Rui (committee member).
Subjects/Keywords: Magnetism; itinerant; ferromagnet; antiferromagnet; quantum critical point; quantum criticality; quantum phase transition
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APA (6th Edition):
Svanidze, E. (2015). Search, Discovery, Synthesis and Characterization of Itinerant Magnets Composed of Non-magnetic Constituents. (Doctoral Dissertation). Rice University. Retrieved from http://hdl.handle.net/1911/88169
Chicago Manual of Style (16th Edition):
Svanidze, Eteri. “Search, Discovery, Synthesis and Characterization of Itinerant Magnets Composed of Non-magnetic Constituents.” 2015. Doctoral Dissertation, Rice University. Accessed January 26, 2021.
http://hdl.handle.net/1911/88169.
MLA Handbook (7th Edition):
Svanidze, Eteri. “Search, Discovery, Synthesis and Characterization of Itinerant Magnets Composed of Non-magnetic Constituents.” 2015. Web. 26 Jan 2021.
Vancouver:
Svanidze E. Search, Discovery, Synthesis and Characterization of Itinerant Magnets Composed of Non-magnetic Constituents. [Internet] [Doctoral dissertation]. Rice University; 2015. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/1911/88169.
Council of Science Editors:
Svanidze E. Search, Discovery, Synthesis and Characterization of Itinerant Magnets Composed of Non-magnetic Constituents. [Doctoral Dissertation]. Rice University; 2015. Available from: http://hdl.handle.net/1911/88169
8.
Mumford, Jesse.
Singularities in a BEC in a double well potential.
Degree: PhD, 2017, McMaster University
URL: http://hdl.handle.net/11375/21978
► This thesis explores the effects singularities have on stationary and dynamical properties of many-body quantum systems. In papers I and II we find that the…
(more)
▼ This thesis explores the effects singularities have on stationary and dynamical properties of many-body
quantum systems. In papers I and II we find that the ground
state suffers a Z2 symmetry breaking
phase transition (PT) when a single impurity
is added to a Bose-Einstein condensate (BEC) in a double well (bosonic Josephson
junction). The PT occurs for a certain value of the BEC-impurity interaction energy,
Λc . A result of the PT is the mean-field dynamics undergo chaotic motion in
phase
space once the symmetry is broken. We determine the critical scaling exponents that
characterize the divergence of the correlation length and fidelity susceptibility at the
PT, finding that the BEC-impurity system belongs to the same universality class as
the Dicke and Lipkin-Meshkov-Glick models (which also describe symmetry breaking
PTs in systems of bosons).
In paper III we study the dynamics of a generic two-mode
quantum field following a
quench where one of the terms in the Hamiltonian is flashed on and off. This model is
relevant to BECs in double wells as well as other simple many-particle systems found
in
quantum optics and optomechanics. We find that when plotted in Fock-space plus
time, the semiclassical wave function develops prominent cusp-shaped structures after
the quench. These structures are singular in the classical limit and we identify them
as catastrophes (as described by the Thom-Arnold catastrophe theory) and show that
they arise from the coalescence of classical (mean-field) trajectories in a path integral
description. Furthermore, close to the cusp the wave function obeys a remarkable set
of scaling relations signifying these structures as examples of universality in
quantum
dynamics. Within the cusp we find a network of vortex-antivortex pairs which are
phase singularities caused by interference. When the mean-field Hamiltonian displays
a Z2 symmetry breaking PT modelled by the Landau theory of PTs we calculate
scaling exponents describing how the separation distance between the members of
each pair diverges as the PT is approached. We also find that the cusp becomes
infinitely stretched out at the PT due to critical slowing down.
In paper IV we investigate in greater detail the morphology of the vortex network
found within cusp catastrophes in many-body wave functions following a quench. In
contrast to the cusp catastrophes studied so far in the literature, these structures live
in Fock space which is fundamentally granular. As such, these cusps represent a new
iii
type of catastrophe, which we term a ‘
quantum catastrophe’. The granularity of Fock
space introduces a new length scale, the
quantum length lq = N −1 which effectively
removes the vortex cores. Nevertheless, a subset of the vortices persist as
phase
singularities as can be shown by integrating the
phase of the wave function around
circuits in Fock-space plus time. Whether or not the vortices survive in a
quantum
catastrophe is governed by the separation of the vortex-antivortex pairs lv ∝ N −3/4
in comparison to lq , i.e.…
Advisors/Committee Members: O'Dell, Duncan, Physics and Astronomy.
Subjects/Keywords: quantum; phase transition; catastrophe theory; many-body systems
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APA (6th Edition):
Mumford, J. (2017). Singularities in a BEC in a double well potential. (Doctoral Dissertation). McMaster University. Retrieved from http://hdl.handle.net/11375/21978
Chicago Manual of Style (16th Edition):
Mumford, Jesse. “Singularities in a BEC in a double well potential.” 2017. Doctoral Dissertation, McMaster University. Accessed January 26, 2021.
http://hdl.handle.net/11375/21978.
MLA Handbook (7th Edition):
Mumford, Jesse. “Singularities in a BEC in a double well potential.” 2017. Web. 26 Jan 2021.
Vancouver:
Mumford J. Singularities in a BEC in a double well potential. [Internet] [Doctoral dissertation]. McMaster University; 2017. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/11375/21978.
Council of Science Editors:
Mumford J. Singularities in a BEC in a double well potential. [Doctoral Dissertation]. McMaster University; 2017. Available from: http://hdl.handle.net/11375/21978
McMaster University
9.
Sur, Shouvik.
Effective Field Theories for Metallic Quantum Critical Points.
Degree: PhD, 2015, McMaster University
URL: http://hdl.handle.net/11375/18412
► In this thesis we study the scaling properties of unconventional metals that arise at quantum critical points using low-energy effective field theories. Due to high…
(more)
▼ In this thesis we study the scaling properties of unconventional metals that arise at quantum
critical points using low-energy effective field theories. Due to high rate of scatterings between
electrons and critical fluctuations of the order parameter associated with spontaneous symmetry
breaking, Landau’s Fermi liquid theory breaks down at the critical points. The theories that
describe these critical points generally flow into strong coupling regimes at low energy in two
space dimensions. Here we develop and utilize renormalization group methods that are suitable
for the interacting non-Fermi liquids. We focus on the critical points arising at excitonic, and
commensurate spin and charge density wave transitions. By controlled analyses we find stable
non-Fermi liquid and marginal Fermi liquid states, and extract the scaling behaviour. The field
theories for the non-Fermi liquids are characterized by symmetry groups, local curvature of the
Fermi surface, the dispersion of the order parameter fluctuations, and dimensions of space and
Fermi surface.
Thesis
Doctor of Philosophy (PhD)
Advisors/Committee Members: Lee, Sung-Sik, Physics and Astronomy.
Subjects/Keywords: Quantum Phase Transition; Metals; Non-Fermi Liquid; Renormalization Group
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APA (6th Edition):
Sur, S. (2015). Effective Field Theories for Metallic Quantum Critical Points. (Doctoral Dissertation). McMaster University. Retrieved from http://hdl.handle.net/11375/18412
Chicago Manual of Style (16th Edition):
Sur, Shouvik. “Effective Field Theories for Metallic Quantum Critical Points.” 2015. Doctoral Dissertation, McMaster University. Accessed January 26, 2021.
http://hdl.handle.net/11375/18412.
MLA Handbook (7th Edition):
Sur, Shouvik. “Effective Field Theories for Metallic Quantum Critical Points.” 2015. Web. 26 Jan 2021.
Vancouver:
Sur S. Effective Field Theories for Metallic Quantum Critical Points. [Internet] [Doctoral dissertation]. McMaster University; 2015. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/11375/18412.
Council of Science Editors:
Sur S. Effective Field Theories for Metallic Quantum Critical Points. [Doctoral Dissertation]. McMaster University; 2015. Available from: http://hdl.handle.net/11375/18412
University of Lethbridge
10.
University of Lethbridge. Faculty of Arts and Science.
Augmenting phase space quantization to introduce additional physical effects
.
Degree: 2017, University of Lethbridge
URL: http://hdl.handle.net/10133/4923
► Quantum mechanics can be done using classical phase space functions and a star product. The state of the system is described by a quasi-probability distribution.…
(more)
▼ Quantum mechanics can be done using classical phase space functions and a star product. The state of the system is described by a quasi-probability distribution.
A classical system can be quantized in phase space in different ways with different quasi-probability distributions and star products. A transition differential operator relates different phase space quantizations.
The objective of this thesis is to introduce additional physical effects into the process of quantization by using the transition operator. As prototypical examples, we first look at the coarse-graining of the Wigner function and the damped simple harmonic oscillator. By generalizing the transition operator and star product to also be functions of the position and momentum, we show that additional physical features beyond damping and coarse-graining can be introduced into a quantum system, including the generalized uncertainty principle of quantum gravity phenomenology, driving forces, and decoherence.
Subjects/Keywords: augmented quantization;
phase space quantum mechanics;
quantization;
star product;
transition operator
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APA (6th Edition):
Science, U. o. L. F. o. A. a. (2017). Augmenting phase space quantization to introduce additional physical effects
. (Thesis). University of Lethbridge. Retrieved from http://hdl.handle.net/10133/4923
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Science, University of Lethbridge. Faculty of Arts and. “Augmenting phase space quantization to introduce additional physical effects
.” 2017. Thesis, University of Lethbridge. Accessed January 26, 2021.
http://hdl.handle.net/10133/4923.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Science, University of Lethbridge. Faculty of Arts and. “Augmenting phase space quantization to introduce additional physical effects
.” 2017. Web. 26 Jan 2021.
Vancouver:
Science UoLFoAa. Augmenting phase space quantization to introduce additional physical effects
. [Internet] [Thesis]. University of Lethbridge; 2017. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/10133/4923.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Science UoLFoAa. Augmenting phase space quantization to introduce additional physical effects
. [Thesis]. University of Lethbridge; 2017. Available from: http://hdl.handle.net/10133/4923
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
University of Toronto
11.
Tian, Di.
Pressure Induced Quantum Phase Transitions.
Degree: PhD, 2017, University of Toronto
URL: http://hdl.handle.net/1807/93046
► Quantum phase transitions are among the most intriguing topics in modern condensed matter physics. Interesting physical phenomena usually emerge in the vicinity of quantum critical…
(more)
▼ Quantum phase transitions are among the most intriguing topics in modern condensed matter physics. Interesting physical phenomena usually emerge in the vicinity of quantum critical points, making the investigation of such quantum systems particularly rewarding.
In this thesis we present studies related to quantum phase transitions in two compounds, FBBO and Sr3Ru2O7, using hydrostatic pressure as the tuning parameter. Pressure is an ideal parameter to tune the strength of various interactions within the sample by changing the lattice constants, but is known to be very challenging to apply experimentally. Therefore a major effort of my PhD is to find out a consistent and systematic approach to prepare such experiments.
FBBO is a neutral organic radical that has been carefully designed to be as metallic as possible at ambient pressure. Nevertheless it is still insulating, and high pressure was required in order to drive this system through the metal-insulator transition. Here, I present strong evidence of the formation of a Fermi liquid ground state under 6.2 GPa [1]. This is the first such observation for a neutral organic radical, after being proposed for decades. In the approach to metallization, we also found intriguing evidence of a low temperature magnetic phase.
The c-axis resistivity of the itinerant metamagnet Sr3Ru2O7 has also been measured under pressure. The initial goal was to search for superconductivity, largely because of the interesting unconventional superconducting ground state found in its close sibling, Sr214. In particular, the c-axis conductivity was measured to rule out possible Sr2RuO4 inclusions within the sample. No superconductivity was found up to the highest pressures of 5.8 GPa and 4.7 GPa respectively in the two independent sets of measurements. Instead, we found that the high temperature resistance falls substantially with increasing pressure, unlike what has been reported for Sr214. The metamagnetic transition shifts rapidly with pressure to higher magnetic field. More importantly, power-law analysis at low temperatures at various pressures indicates that the strength of the electron-electron interaction decays rapidly with increasing pressure. This offers a natural explanation for our failure to induce superconductivity at high pressures.
2018-12-19 00:00:00
Advisors/Committee Members: Julian, Stephen R, Physics.
Subjects/Keywords: Anvil cell; High pressure; Metal insulator transition; Quantum phase transition; Superconductivity; 0605
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APA (6th Edition):
Tian, D. (2017). Pressure Induced Quantum Phase Transitions. (Doctoral Dissertation). University of Toronto. Retrieved from http://hdl.handle.net/1807/93046
Chicago Manual of Style (16th Edition):
Tian, Di. “Pressure Induced Quantum Phase Transitions.” 2017. Doctoral Dissertation, University of Toronto. Accessed January 26, 2021.
http://hdl.handle.net/1807/93046.
MLA Handbook (7th Edition):
Tian, Di. “Pressure Induced Quantum Phase Transitions.” 2017. Web. 26 Jan 2021.
Vancouver:
Tian D. Pressure Induced Quantum Phase Transitions. [Internet] [Doctoral dissertation]. University of Toronto; 2017. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/1807/93046.
Council of Science Editors:
Tian D. Pressure Induced Quantum Phase Transitions. [Doctoral Dissertation]. University of Toronto; 2017. Available from: http://hdl.handle.net/1807/93046
University of Cambridge
12.
Haines, Charles Robert Sebastian.
Pressure tuned magnetism in d- and f-electron materials.
Degree: PhD, 2012, University of Cambridge
URL: https://doi.org/10.17863/CAM.30351
;
https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609979
► Quantum phase transitions (QPT) on the border of magnetism have provided a fertile hunting ground for the discovery of new states of matter, for example;…
(more)
▼ Quantum phase transitions (QPT) on the border of magnetism have provided a fertile hunting ground for the discovery of new states of matter, for example; the marginal Fermi Liquid and non Fermi Liquid states as well high TC cuprate and magnetically mediated superconductivity. In this thesis I present work on three materials in which it may be possible to tune the system through a magnetic QPT with the application of hydrostatic pressure. Although the details of the underlying physics are different in each of the materials, they are linked by the possibility of finding new states on the border of magnetism. Applying hydrostatic pressure, we have suppressed the ferromagnetic (FM) transition in metallic Fe2P to very low temperature and to a potential QPT. Counter-intuitive broadening of the magnetic hysteresis leading up to the FM-AFM QPT may well be a crucial clue as to the nature of the model needed to understand this phase transition. A sharp increase in the quasi-particle scattering cross-section as well as the residual resistivity accompany a departure from the quadratic temperature dependence of the resistivity. This possible deviation from Fermi liquid behaviour is stable over a significant range of temperature. The unexplained upturn in the resistivity of CeGe that accompanies the AFM transition was studied under pressure. Pressure increased the residual resistivity as well as decreasing the relative size of the upturn, but had a moderate effect on the Neel temperature. The insensitivity of the N\acute eel temperature to pressure has been compared to its relative sensitivity to applied feld. The existence of the upturn and its evolution with pressure and applied feld can reasonably be argued to be due to the details of the electron band structure in the system. By applying pressure we have drastically reduced the resistivity of the insulating antiferromagnet NiPS3. Concurrent work on FePS3 has shown metallisation under pressure. It seems reasonable to speculate that NiPS3 may also metallise at higher pressure. The energy gap is narrowed in both materials as pressure is increased. Magnetisation measurements have revealed a low temperature upturn indicating some possible ferromagnetic component or proximity to another magnetic state. A peak in the magnetisation is also seen at 45K in zero-feld cooled measurements. Both of these features point to a system with a complex magnetic ground state.
Subjects/Keywords: 530; High Pressure; Strongly Correlated; Quantum Criticality; Heavy Fermion; Quantum Phase Transition
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APA (6th Edition):
Haines, C. R. S. (2012). Pressure tuned magnetism in d- and f-electron materials. (Doctoral Dissertation). University of Cambridge. Retrieved from https://doi.org/10.17863/CAM.30351 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609979
Chicago Manual of Style (16th Edition):
Haines, Charles Robert Sebastian. “Pressure tuned magnetism in d- and f-electron materials.” 2012. Doctoral Dissertation, University of Cambridge. Accessed January 26, 2021.
https://doi.org/10.17863/CAM.30351 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609979.
MLA Handbook (7th Edition):
Haines, Charles Robert Sebastian. “Pressure tuned magnetism in d- and f-electron materials.” 2012. Web. 26 Jan 2021.
Vancouver:
Haines CRS. Pressure tuned magnetism in d- and f-electron materials. [Internet] [Doctoral dissertation]. University of Cambridge; 2012. [cited 2021 Jan 26].
Available from: https://doi.org/10.17863/CAM.30351 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609979.
Council of Science Editors:
Haines CRS. Pressure tuned magnetism in d- and f-electron materials. [Doctoral Dissertation]. University of Cambridge; 2012. Available from: https://doi.org/10.17863/CAM.30351 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609979
Colorado School of Mines
13.
Alcala, Diego A.
Macroscopic quantum tunneling and quantum many-body dynamics in Bose-Einstein condensates.
Degree: PhD, Physics, 2020, Colorado School of Mines
URL: http://hdl.handle.net/11124/174203
► Quantum mechanics revolutionized the previous century, not only in technology with lasers and semiconductors but also our fundamental view of the world with Bell's inequality…
(more)
▼ Quantum mechanics revolutionized the previous century, not only in technology with lasers and semiconductors but also our fundamental view of the world with Bell's inequality and entanglement.
Quantum tunneling was the first experimental verification of
quantum mechanics, by solving the mystery of radioactive decay, that a particle can escape the nucleus without sufficient energy to overcome the classical energy barrier. In this century, many-body
quantum mechanics is bringing about a second revolution, with the possibility of
quantum simulators,
quantum computers, and a deeper understanding the nature. However, in order to fully harness the power of these systems, a detailed understanding of many-body effects is required, such as fluctuations, correlations, and entanglement. In this thesis, we seek to understand these observables in the context of macroscopic
quantum tunneling. We quantify the macroscopic
quantum tunneling dynamics, showing how interactions alter tunneling and
quantum phase transitions modify non-equilibrium dynamics, providing a road maps of future experiments. The first experimental realization of mean-field interactions producing non-exponential decay of a tunneling Bose-Einstein condensate has been achieved. We develop an effective semi-classical model which accounts for the repulsive atom-atom interactions via an additional mean-field potential. This captures the 3D
quantum tunneling via classical oscillations in an effective 1D trap and tunneling through a barrier with time-dependent height due to mean-field interactions. Mean-field treatments work well for Bose-Einstein condensates with negligible many-body effects, such as fragmentation, depletion, and fluctuations away from the mean. We show how a Bose-Einstein condensate with non-negligible fragmentation and depletion can be described with a renormalized mean-field. This suggest mean-field models are more widely applicable than previously thought, and that many-body physics may be hiding in such experiments and systems. Next, we explicitly look at the dynamics of many-body tunneling from a meta-stable trap, described by the Bose-Hubbard Hamiltonian in the superfluid
quantum phase. The many-body physics are simulated using matrix product state methods, which allow exploration of lowly-entangled dynamics via data compression methods, and can calculate a wide range of
quantum observables, like number fluctuations, correlations, and entanglement entropy. We compare many-body and mean-field dynamics, explicitly showing many-body tunneling times converge to mean-field tunneling times with increasing number of atoms in the system. We find rich dynamics with different time scales for the escape time, fluctuations, and
quantum entropy in the system. With a firm grasp on the superfluid dynamics in the Bose-Hubbard Hamiltonian, we turn our attention to the superfluid to Mott insulating
quantum phase transition, and understanding how the initial
quantum phase alters macroscopic
quantum tunneling. We examine this for both the double-well and
quantum…
Advisors/Committee Members: Carr, Lincoln D. (advisor), Wu, Mingzhong (advisor), Tenorio, Luis (committee member), Pankavich, Stephen (committee member), Flammer, P. David (committee member).
Subjects/Keywords: many-body dynamics; quantum tunneling; Bose-Hubbard model; ultracold atoms; quantum phase transition
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APA ·
Chicago ·
MLA ·
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APA (6th Edition):
Alcala, D. A. (2020). Macroscopic quantum tunneling and quantum many-body dynamics in Bose-Einstein condensates. (Doctoral Dissertation). Colorado School of Mines. Retrieved from http://hdl.handle.net/11124/174203
Chicago Manual of Style (16th Edition):
Alcala, Diego A. “Macroscopic quantum tunneling and quantum many-body dynamics in Bose-Einstein condensates.” 2020. Doctoral Dissertation, Colorado School of Mines. Accessed January 26, 2021.
http://hdl.handle.net/11124/174203.
MLA Handbook (7th Edition):
Alcala, Diego A. “Macroscopic quantum tunneling and quantum many-body dynamics in Bose-Einstein condensates.” 2020. Web. 26 Jan 2021.
Vancouver:
Alcala DA. Macroscopic quantum tunneling and quantum many-body dynamics in Bose-Einstein condensates. [Internet] [Doctoral dissertation]. Colorado School of Mines; 2020. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/11124/174203.
Council of Science Editors:
Alcala DA. Macroscopic quantum tunneling and quantum many-body dynamics in Bose-Einstein condensates. [Doctoral Dissertation]. Colorado School of Mines; 2020. Available from: http://hdl.handle.net/11124/174203
University of Cambridge
14.
Chen, Xiaoye.
Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2.
Degree: PhD, 2017, University of Cambridge
URL: https://www.repository.cam.ac.uk/handle/1810/270025
► Materials in proximity to quantum critical points (QCPs) experience strong fluctuations in the order parameter associated with the transition and often, as a result, display…
(more)
▼ Materials in proximity to quantum critical points (QCPs) experience strong fluctuations in the order parameter associated with the transition and often, as a result, display interesting properties. In this dissertation, we have used a variety of experimental probes such as Shubnikov-de Haas quantum oscillations, thermal conductivity and heat capacity, to better understand two such materials — A3T4Sn13 and YFe2Ge2.
A3T4Sn13 (A = Ca, Sr; T = Ir, Rh) is a family of quasi-skutterudite superconductors with moderate Tc’s between 4 and 8 K. Although the superconductivity is believed to be phonon-mediated with s-wave pairing symmetry, an unusual second-order structural transition makes this material family fascinating to study. Whether this structural transition is a result of three distortions with perpendicular wavevectors resulting in a cubic-to-cubic transformation, or each wavevector acting independently giving rise to cubic-to-tetragonal transformations and formation of twinned domains is a disputed issue. We have measured quantum oscillations in the resistivity of Sr3Ir4Sn13 and compared it to density functional theory (DFT) calculations for both scenarios. Our results strongly suggest that the former interpretation is correct.
The structural transition temperature T^* in A3T4Sn13 can be suppressed to zero by tuning with physical or chemical pressure. In (CaxSr1−x)3Rh4Sn13, the quantum critical point can be accessed purely by chemical substitution at x ~ 0.9. In the vicinity of the QCP, we expect large fluctuations of the order parameter at low temperatures, which for a structural transition could manifest as a structural disorder. We have measured thermal conductivity at temperatures much lower than Tc and found that it is well described by a single power law with suppressed exponents near the QCP. The heat capacity, however, remains ~ T3. After excluding conventional phonon scattering mechanisms, we propose the possibility of intrinsic quasi-static spatial disorder that is related to the structural QCP.
YFe2Ge2 is closely linked to the “122” family of iron-based superconductors like KFe2As2, although it has a significantly lower Tc ~ 1 K. It has a rather three-dimensional Fermi surface which closely resembles that of KFe2As2 in the pressure-induced collapsed tetragonal phase. YFe2Ge2 is in proximity to several types of magnetic order which are predicted by DFT calculations to have lower energy than the non-spin polarised case. Even though YFe2Ge2 is non-magnetic, its superconductivity could be strongly affected by magnetic fluctuations. Through a collaboration with researchers at the University of Waterloo, we have measured the thermal conductivity of YFe2Ge2 down to millikelvin temperatures and up to 2.5 T in field. Our results suggest that YFe2Ge2 is a nodal superconductor. This result could assist in the explanation of the unconventional superconductivity in iron-based superconductors.
Subjects/Keywords: superconductivity; structural transition; quantum criticality; QCP; phase transition; thermal conductivity; quantum oscillations; phonon mean free path; phonon scattering
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APA ·
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MLA ·
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CSE |
Export
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APA (6th Edition):
Chen, X. (2017). Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2. (Doctoral Dissertation). University of Cambridge. Retrieved from https://www.repository.cam.ac.uk/handle/1810/270025
Chicago Manual of Style (16th Edition):
Chen, Xiaoye. “Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2.” 2017. Doctoral Dissertation, University of Cambridge. Accessed January 26, 2021.
https://www.repository.cam.ac.uk/handle/1810/270025.
MLA Handbook (7th Edition):
Chen, Xiaoye. “Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2.” 2017. Web. 26 Jan 2021.
Vancouver:
Chen X. Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2. [Internet] [Doctoral dissertation]. University of Cambridge; 2017. [cited 2021 Jan 26].
Available from: https://www.repository.cam.ac.uk/handle/1810/270025.
Council of Science Editors:
Chen X. Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2. [Doctoral Dissertation]. University of Cambridge; 2017. Available from: https://www.repository.cam.ac.uk/handle/1810/270025
Rice University
15.
Wu, Jianda.
Research on Dynamics and Thermodynamics near Quantum Critical Points.
Degree: PhD, Natural Sciences, 2014, Rice University
URL: http://hdl.handle.net/1911/88431
► Quantum phase transition arises in general as second order phase transition at zero temperature, tuned by a non-thermal parameter such as pressure, doping or a…
(more)
▼ Quantum phase transition arises in general as second order
phase transition at zero temperature, tuned by a non-thermal parameter such as pressure, doping or a magnetic field. The point in the
phase diagram of the material in which different phases meet is called a
quantum critical point (QCP). Physics around QCPs are of extensive current interest because the critical
quantum fluctuations influence the physical properties in a wide temperature range (
quantum criticality), and are believed to be responsible for many emergent physical properties such as non-Fermi liquids and unconventional superconductivity. In this research we explore dynamics and thermodynamics near QCPs via investigating three classes of models, which all have real material correspondence. Specifically first, we study local dynamics in a perturbed
quantum critical Ising chain with E8 symmetry, where we show the local dynamical spin susceptibility has a singular dependence on frequency, but differs from the diffusion form. The nuclear magnetic resonance (NMR) relaxation rate at low temperatures depends exponentially on the inverse temperature, whose prefactor we also determine. We propose NMR experiments as a means to further test the applicability of the E8 description for CoNb2O6. Second, we investigate the thermodynamic properties of itinerant ferromagnets near
quantum critical points, described by the
quantum Landau-Ginzburg theory. We provide a regularized perturbative renormalization group procedure to calculate the free energy. We further carry out numerical calculations on thermodynamic quantities, capturing not only the leading critical behaviors, but also the subleading and nonsingular contributions. We demonstrate various thermodynamic signatures of
quantum criticality, including the entropy accumulation effect and the divergence of the specific heat coefficient. A detailed comparison to the recent experimental results on an itinerant ferromagnet Sr3Ru2O7 is also presented. Third, we explore Ising-nematic and magnetic phases and their transitions in iso-electronically doped iron pnictides by carrying out a large-N study of an effective low-energy Ginzburg-Landau model for these systems. We demonstrate that the magnetic and Ising orders transitions are concurrent at zero temperature, and both transitions are weakly first-order, which is consistent with RG-based prediction and experimental observations.
Advisors/Committee Members: Si, Qimiao (advisor), Nevidomskyy, Andriy (committee member), Deem, Michael (committee member).
Subjects/Keywords: Quantum phase transition; Quantum criticality; E8 model; Itinerant spin-density-wave transition; Perturbative renormalization group; Iron pnictides; Large-N approach
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APA ·
Chicago ·
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Export
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APA (6th Edition):
Wu, J. (2014). Research on Dynamics and Thermodynamics near Quantum Critical Points. (Doctoral Dissertation). Rice University. Retrieved from http://hdl.handle.net/1911/88431
Chicago Manual of Style (16th Edition):
Wu, Jianda. “Research on Dynamics and Thermodynamics near Quantum Critical Points.” 2014. Doctoral Dissertation, Rice University. Accessed January 26, 2021.
http://hdl.handle.net/1911/88431.
MLA Handbook (7th Edition):
Wu, Jianda. “Research on Dynamics and Thermodynamics near Quantum Critical Points.” 2014. Web. 26 Jan 2021.
Vancouver:
Wu J. Research on Dynamics and Thermodynamics near Quantum Critical Points. [Internet] [Doctoral dissertation]. Rice University; 2014. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/1911/88431.
Council of Science Editors:
Wu J. Research on Dynamics and Thermodynamics near Quantum Critical Points. [Doctoral Dissertation]. Rice University; 2014. Available from: http://hdl.handle.net/1911/88431
16.
Chen, Xiaoye.
Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2.
Degree: PhD, 2017, University of Cambridge
URL: https://doi.org/10.17863/CAM.16865
;
https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.744358
► Materials in proximity to quantum critical points (QCPs) experience strong fluctuations in the order parameter associated with the transition and often, as a result, display…
(more)
▼ Materials in proximity to quantum critical points (QCPs) experience strong fluctuations in the order parameter associated with the transition and often, as a result, display interesting properties. In this dissertation, we have used a variety of experimental probes such as Shubnikov-de Haas quantum oscillations, thermal conductivity and heat capacity, to better understand two such materials — A3T4Sn13 and YFe2Ge2. A3T4Sn13 (A = Ca, Sr; T = Ir, Rh) is a family of quasi-skutterudite superconductors with moderate Tc’s between 4 and 8 K. Although the superconductivity is believed to be phonon-mediated with s-wave pairing symmetry, an unusual second-order structural transition makes this material family fascinating to study. Whether this structural transition is a result of three distortions with perpendicular wavevectors resulting in a cubic-to-cubic transformation, or each wavevector acting independently giving rise to cubic-to-tetragonal transformations and formation of twinned domains is a disputed issue. We have measured quantum oscillations in the resistivity of Sr3Ir4Sn13 and compared it to density functional theory (DFT) calculations for both scenarios. Our results strongly suggest that the former interpretation is correct. The structural transition temperature T^* in A3T4Sn13 can be suppressed to zero by tuning with physical or chemical pressure. In (CaxSr1−x)3Rh4Sn13, the quantum critical point can be accessed purely by chemical substitution at x ~ 0.9. In the vicinity of the QCP, we expect large fluctuations of the order parameter at low temperatures, which for a structural transition could manifest as a structural disorder. We have measured thermal conductivity at temperatures much lower than Tc and found that it is well described by a single power law with suppressed exponents near the QCP. The heat capacity, however, remains ~ T3. After excluding conventional phonon scattering mechanisms, we propose the possibility of intrinsic quasi-static spatial disorder that is related to the structural QCP. YFe2Ge2 is closely linked to the “122” family of iron-based superconductors like KFe2As2, although it has a significantly lower Tc ~ 1 K. It has a rather three-dimensional Fermi surface which closely resembles that of KFe2As2 in the pressure-induced collapsed tetragonal phase. YFe2Ge2 is in proximity to several types of magnetic order which are predicted by DFT calculations to have lower energy than the non-spin polarised case. Even though YFe2Ge2 is non-magnetic, its superconductivity could be strongly affected by magnetic fluctuations. Through a collaboration with researchers at the University of Waterloo, we have measured the thermal conductivity of YFe2Ge2 down to millikelvin temperatures and up to 2.5 T in field. Our results suggest that YFe2Ge2 is a nodal superconductor. This result could assist in the explanation of the unconventional superconductivity in iron-based superconductors.
Subjects/Keywords: 537.6; superconductivity; structural transition; quantum criticality; QCP; phase transition; thermal conductivity; quantum oscillations; phonon mean free path; phonon scattering
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APA ·
Chicago ·
MLA ·
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CSE |
Export
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Manager
APA (6th Edition):
Chen, X. (2017). Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2. (Doctoral Dissertation). University of Cambridge. Retrieved from https://doi.org/10.17863/CAM.16865 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.744358
Chicago Manual of Style (16th Edition):
Chen, Xiaoye. “Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2.” 2017. Doctoral Dissertation, University of Cambridge. Accessed January 26, 2021.
https://doi.org/10.17863/CAM.16865 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.744358.
MLA Handbook (7th Edition):
Chen, Xiaoye. “Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2.” 2017. Web. 26 Jan 2021.
Vancouver:
Chen X. Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2. [Internet] [Doctoral dissertation]. University of Cambridge; 2017. [cited 2021 Jan 26].
Available from: https://doi.org/10.17863/CAM.16865 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.744358.
Council of Science Editors:
Chen X. Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2. [Doctoral Dissertation]. University of Cambridge; 2017. Available from: https://doi.org/10.17863/CAM.16865 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.744358
17.
Hurand, Simon.
Contrôle de la supraconductivité à l'interface d'oxydes LaAlO3/SrTiO3 par effet de champ électrique : Field-effect control of superconductivity at LaAlO3/SrTiO3 oxides interface.
Degree: Docteur es, Physique, 2015, Université Pierre et Marie Curie – Paris VI
URL: http://www.theses.fr/2015PA066014
► Cette thèse s'intéresse à l'étude de la supraconductivité bidimensionnelle à l'interface entre les oxydes LaAlO3 et SrTiO3 contrôlée par effet de champ électrique. Lorsqu'on fait…
(more)
▼ Cette thèse s'intéresse à l'étude de la supraconductivité bidimensionnelle à l'interface entre les oxydes LaAlO3 et SrTiO3 contrôlée par effet de champ électrique. Lorsqu'on fait croître une couche mince de quelques mailles atomiques de LaAlO3 sur un substrat de SrTiO3, l'interface devient conductrice, et même supraconductrice au-dessous de 300mK, bien que ces deux oxydes de structure pérovskite soient des isolants. Il se forme ainsi un gaz bidimensionnel d'électrons de haute mobilité, dont les propriétés - supraconductivité et fort couplage spin-orbite de type Rashba - peuvent être contrôlées par effet de champ électrique à l'aide d'une Back Gate. Nous avons étudié cette supraconductivité bidimensionnelle par trois approches expérimentales différentes : l'étude de la transition supraconductrice en température à l'aide du modèle de Berezinskii-Kosterlitz-Thouless incluant une distribution inhomogène de rigidité ; l'analyse par le groupe de renormalisation de la transition de phase quantique supraconducteur-isolant induite par un champ magnétique perpendiculaire à l'interface selon le modèle de Spivak, Oreto et Kivelson ; et enfin l'étude de l'hystérèse du courant critique ainsi que de sa nature probabiliste dans le cadre du modèle RCSJ. Nous proposons donc de considérer l'interface comme un réseau de flaques supraconductrices couplées par effet Josephson à travers un gaz 2D métallique, dont la transition est régie par le modèle XY des fluctuations de phase. Enfin, nous avons démontré pour la première fois la possibilité de contrôler les propriétés du gaz 2D à l'aide d'une Top Gate, et comparé les effets des deux grilles (Top ou Back Gate).
In this PhD work, we study the field-effect modulated two-dimensional superconductivity at the LaAlO3/SrTiO3 oxides hetero-interface. When one grows epitaxially a few unit cells thin film of LaAlO3 on a SrTiO3 substrate, the interface becomes conducting, and even superconducting below 300mK, although these two perovskite oxides are insulators. The properties of this high-mobility two-dimensional electron gas – superconductivity and strong Rashba-type spin-orbit coupling - can be field-effect modulated by the mean of a Back Gate. We have investigated this two-dimensional superconductivity through three different experimental approaches : the temperature-driven transition with the Berezinskii-Kosterlitz-Thouless model including an inhomogeneous distribution of rigidity ; the finite-size scaling analysis of the superconductor-to-insulator quantum phase transition induced by a perpendicular magnetic field using the model developed by Spivak, Oreto and Kivelson ; and finally the measure of the hysteretic and stochastic properties of the critical current in the framework of the RCSJ model. We hence propose to consider this 2D electron gas as an inhomogeneous network of superconducting puddles coupled to one another by Josephson effect through a normal metallic matrix, which transition is dominated by the XY model of the phase fluctuations. Finally, we demonstrated for the first time…
Advisors/Committee Members: Bergeal, Nicolas (thesis director), Lesueur, Jérôme (thesis director).
Subjects/Keywords: Supraconductivité; Laalo3/srtio3; Spin-Orbite; Bkt; Transition de phase quantique; Switching; Superconductivity; Quantum phase transition; 530
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APA ·
Chicago ·
MLA ·
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to Zotero / EndNote / Reference
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APA (6th Edition):
Hurand, S. (2015). Contrôle de la supraconductivité à l'interface d'oxydes LaAlO3/SrTiO3 par effet de champ électrique : Field-effect control of superconductivity at LaAlO3/SrTiO3 oxides interface. (Doctoral Dissertation). Université Pierre et Marie Curie – Paris VI. Retrieved from http://www.theses.fr/2015PA066014
Chicago Manual of Style (16th Edition):
Hurand, Simon. “Contrôle de la supraconductivité à l'interface d'oxydes LaAlO3/SrTiO3 par effet de champ électrique : Field-effect control of superconductivity at LaAlO3/SrTiO3 oxides interface.” 2015. Doctoral Dissertation, Université Pierre et Marie Curie – Paris VI. Accessed January 26, 2021.
http://www.theses.fr/2015PA066014.
MLA Handbook (7th Edition):
Hurand, Simon. “Contrôle de la supraconductivité à l'interface d'oxydes LaAlO3/SrTiO3 par effet de champ électrique : Field-effect control of superconductivity at LaAlO3/SrTiO3 oxides interface.” 2015. Web. 26 Jan 2021.
Vancouver:
Hurand S. Contrôle de la supraconductivité à l'interface d'oxydes LaAlO3/SrTiO3 par effet de champ électrique : Field-effect control of superconductivity at LaAlO3/SrTiO3 oxides interface. [Internet] [Doctoral dissertation]. Université Pierre et Marie Curie – Paris VI; 2015. [cited 2021 Jan 26].
Available from: http://www.theses.fr/2015PA066014.
Council of Science Editors:
Hurand S. Contrôle de la supraconductivité à l'interface d'oxydes LaAlO3/SrTiO3 par effet de champ électrique : Field-effect control of superconductivity at LaAlO3/SrTiO3 oxides interface. [Doctoral Dissertation]. Université Pierre et Marie Curie – Paris VI; 2015. Available from: http://www.theses.fr/2015PA066014
Kent State University
18.
Gebretsadik, Adane Samuel, Gebretsadik.
INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED
ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION.
Degree: PhD, College of Arts and Sciences / Department of
Physics, 2018, Kent State University
URL: http://rave.ohiolink.edu/etdc/view?acc_num=kent1527609152939816
► This dissertation presents a detailed study of the structural and magnetic properties of selected ferromagnetic alloys to probe the impact of "disorder" on quantum phase…
(more)
▼ This dissertation presents a detailed study of the
structural and magnetic properties of selected ferromagnetic alloys
to probe the impact of "disorder" on
quantum phase transition. The
interplay between chemical and magnetic disorder close to a
ferromagnetic
quantum phase transition is investigated in the
d-metal alloy Ni(1-x)V(x) and the f-metal alloys, CeT(1-x)Rh(x)
(with T=Pd and Pt) by muon spin rotation (muSR) and wide-angle
neutron scattering with pair distribution function (PDF) analysis.
I present muon spin rotation (muSR) data and wide-angle neutron
diffraction data with pair distribution function (PDF) analysis of
two ferromagnetic alloys that can be driven to a paramagnetic
phase
by chemical substitution. Both systems, Ni(1-x)V(x), where the
ferromagnetic order is suppressed at xc=0.116 and CeT(1-x)Rh(x)
with xc>0.5 show indications that magnetic inhomogeneities play
an important role for this
quantum phase transition. muSR data of
Ni(1-x)V(x) directly distinguishes finite magnetic clusters from
long range magnetic order and therefore gives strong evidence for a
quantum Griffiths
phase extending into the ferromagnetic
phase.
Since the location of the V is crucial for creating the magnetic
inhomogeneities, a structural investigation focusing on local pair
correlations clarifies how much chemical disorder is present. It
confirms that the Ni(1-x)V(x) powder samples up to x=0.15
crystallize in a random alloy fcc structure. Simulations of the
local PDF with other models give inferior results. This strongly
supports that in Ni-V the magnetic clusters originate from Ni-rich
regions created from random occupation rather than from chemical
clusters. The PDF analysis of the neutron data of the CeRh-alloys
finds structural abnormalities that are directly related to
magnetic inhomogeneities. All polycrystalline CeT(1-x)Rh(x) samples
with 0.2< x<0.8 crystallize in the same CrB structure but
show different additional phases in small concentrations. The
change of lattice constants and atomic displacement parameters
towards higher x indicate a large variation in Ce-Rh bond lengths.
This disorder originates from the different Ce neighbor atoms,
explaining nonmagnetic Ce impurities and variations in Kondo
temperatures. In both systems, a direct relationship between
chemical and magnetic structure is revealed that clarifies the
origin of disorder for the ferromagnetic
quantum phase
transition.
Advisors/Committee Members: Schroeder, Almut (Advisor).
Subjects/Keywords: Physics; quantum phase transition; disorder; magnetic clusters; quantum Griffiths phase; neutron scattering; pair distribution function; muon spin rotation
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APA ·
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MLA ·
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APA (6th Edition):
Gebretsadik, Adane Samuel, G. (2018). INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED
ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION. (Doctoral Dissertation). Kent State University. Retrieved from http://rave.ohiolink.edu/etdc/view?acc_num=kent1527609152939816
Chicago Manual of Style (16th Edition):
Gebretsadik, Adane Samuel, Gebretsadik. “INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED
ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION.” 2018. Doctoral Dissertation, Kent State University. Accessed January 26, 2021.
http://rave.ohiolink.edu/etdc/view?acc_num=kent1527609152939816.
MLA Handbook (7th Edition):
Gebretsadik, Adane Samuel, Gebretsadik. “INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED
ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION.” 2018. Web. 26 Jan 2021.
Vancouver:
Gebretsadik, Adane Samuel G. INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED
ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION. [Internet] [Doctoral dissertation]. Kent State University; 2018. [cited 2021 Jan 26].
Available from: http://rave.ohiolink.edu/etdc/view?acc_num=kent1527609152939816.
Council of Science Editors:
Gebretsadik, Adane Samuel G. INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED
ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION. [Doctoral Dissertation]. Kent State University; 2018. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=kent1527609152939816
University of California – Riverside
19.
Hou, Changtao.
Renormalization Group Analysis of 2+1D Quantum XY Model With Dissipation.
Degree: Physics, 2016, University of California – Riverside
URL: http://www.escholarship.org/uc/item/3mf1k75p
► This thesis present the recently theoretical and numerical results on 2D dissipative quantum XY model. The two-dimensional quantum XY model is applicable to the quantum…
(more)
▼ This thesis present the recently theoretical and numerical results on 2D dissipative quantum XY model. The two-dimensional quantum XY model is applicable to the quantum critical properties of several experimental systems, such as superconductor to insulator transitions, ferromagnetic and antiferromagnetic transitions in metals, and loop current order transition in the cuprates. Renormalization group methods are applied to solve the reformulated ac- tion of the original model in terms of two type topological excitations: vortices and warps. The calculations explain the extraordinary properties of the model studied through quan- tum Monte Carlo simulations: the separability of the correlation function in space and time, the correlation length in space proportional to logarithm of the correlation length in time near the transition from disordered phase to ordered phase. The running dynamical critical exponent is introduced to address the anisotropy between time and space. The effects of anisotropy fields have been examined through renormalization group method. The transi- tion from disordered phase to ordered phase of this model has been studied by quantum Monte Carlo. The divergence of temporal correlation length in function of (Kc − K)/Kc is examined by numerical simulation. The logarithmic relation between temporal correlation length and spacial correlation length is further confirmed. Also, the same logarithmic rela- tion for different correlation function with different space separation is found and implicitly confirmed the separability of correlation function in space and time.
Subjects/Keywords: Physics; Condensed matter physics; Theoretical physics; High Temperature Superconductor; Quantum Criticality; Quantum Phase Transition; Quantum XY Model; Renormalization Group Method
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MLA ·
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CSE |
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Manager
APA (6th Edition):
Hou, C. (2016). Renormalization Group Analysis of 2+1D Quantum XY Model With Dissipation. (Thesis). University of California – Riverside. Retrieved from http://www.escholarship.org/uc/item/3mf1k75p
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Hou, Changtao. “Renormalization Group Analysis of 2+1D Quantum XY Model With Dissipation.” 2016. Thesis, University of California – Riverside. Accessed January 26, 2021.
http://www.escholarship.org/uc/item/3mf1k75p.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Hou, Changtao. “Renormalization Group Analysis of 2+1D Quantum XY Model With Dissipation.” 2016. Web. 26 Jan 2021.
Vancouver:
Hou C. Renormalization Group Analysis of 2+1D Quantum XY Model With Dissipation. [Internet] [Thesis]. University of California – Riverside; 2016. [cited 2021 Jan 26].
Available from: http://www.escholarship.org/uc/item/3mf1k75p.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Hou C. Renormalization Group Analysis of 2+1D Quantum XY Model With Dissipation. [Thesis]. University of California – Riverside; 2016. Available from: http://www.escholarship.org/uc/item/3mf1k75p
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
University of Florida
20.
Chowdhury, Tathagata.
A Study of Quantum Phase Transitions in Quantum Impurity Systems.
Degree: PhD, Physics, 2015, University of Florida
URL: https://ufdc.ufl.edu/UFE0049560
► Kondo and Anderson impurity models with a pseudogap density of states that vanishes at the Fermi energy, feature a continuous quantum phase transition (QPT) that…
(more)
▼ Kondo and Anderson impurity models with a pseudogap density of states that vanishes at the Fermi energy, feature a continuous
quantum phase transition (QPT) that separates a local-moment
phase from strong-coupling phases. The
quantum critical points (QCPs) exhibit critical Kondo destruction, which is of current interest in connection with heavy-fermion
quantum criticality. Motivated by recent experimental and theoretical developments, the numerical renormalization-group technique is used to study the
quantum criticality in several pertinent models that demonstrate a QPT.
Advisors/Committee Members: INGERSENT,J KEVIN (committee chair), HERSHFIELD,SELMAN PHILIP (committee member), HIRSCHFELD,PETER J (committee member), HENNIG,RICHARD (committee member).
Subjects/Keywords: Conduction bands; Critical points; Electrons; Entropy; Impurities; Magnetic fields; Magnetism; Phase transitions; Quantum dots; Quantum entanglement; anderson-model – condensed-matter – entanglement – graphene – kondo – quantum-criticality – quantum-phase-transition – strongly-correlated
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APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Chowdhury, T. (2015). A Study of Quantum Phase Transitions in Quantum Impurity Systems. (Doctoral Dissertation). University of Florida. Retrieved from https://ufdc.ufl.edu/UFE0049560
Chicago Manual of Style (16th Edition):
Chowdhury, Tathagata. “A Study of Quantum Phase Transitions in Quantum Impurity Systems.” 2015. Doctoral Dissertation, University of Florida. Accessed January 26, 2021.
https://ufdc.ufl.edu/UFE0049560.
MLA Handbook (7th Edition):
Chowdhury, Tathagata. “A Study of Quantum Phase Transitions in Quantum Impurity Systems.” 2015. Web. 26 Jan 2021.
Vancouver:
Chowdhury T. A Study of Quantum Phase Transitions in Quantum Impurity Systems. [Internet] [Doctoral dissertation]. University of Florida; 2015. [cited 2021 Jan 26].
Available from: https://ufdc.ufl.edu/UFE0049560.
Council of Science Editors:
Chowdhury T. A Study of Quantum Phase Transitions in Quantum Impurity Systems. [Doctoral Dissertation]. University of Florida; 2015. Available from: https://ufdc.ufl.edu/UFE0049560
NSYSU
21.
Hsiao, Chin-Lun.
Quantum anomalous Hall effect in the Haldane-Rashba system.
Degree: Master, Physics, 2014, NSYSU
URL: http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0610114-201805
► We study the possible Chern insulator phase transitions in the Haldane-Rashba system. These systems could be established on single-layer graphene and realized by using the…
(more)
▼ We study the possible Chern insulator
phase transitions in the Haldane-Rashba system. These systems could be established on single-layer graphene and realized by using the ultracold atoms. Therefore, we investigate the
quantum anomalous Hall effect in the Haldane-Rashba systm. We first describe how to construct tight-binding model Hamiltonian and obtain the Dirac points. We then show the electronic band structure and the corresponding wave functions of electrons. By using the boundary of
phase transformation we study the change in Chern number in Haldane-Rashba system. Finally, we discuss the variation of Chern number values and its corresponding
phase transitions.
Advisors/Committee Members: Tsung-Wei Chen (committee member), Shiow-Fon Tsay (chair), Wang-Chuang Kuo (chair), Chong-Der Hu (chair).
Subjects/Keywords: Hall effect; Anomalous; Spin; Spin-orbit interaction; Chern number; Quantum phase transition
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APA ·
Chicago ·
MLA ·
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Export
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APA (6th Edition):
Hsiao, C. (2014). Quantum anomalous Hall effect in the Haldane-Rashba system. (Thesis). NSYSU. Retrieved from http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0610114-201805
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Hsiao, Chin-Lun. “Quantum anomalous Hall effect in the Haldane-Rashba system.” 2014. Thesis, NSYSU. Accessed January 26, 2021.
http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0610114-201805.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Hsiao, Chin-Lun. “Quantum anomalous Hall effect in the Haldane-Rashba system.” 2014. Web. 26 Jan 2021.
Vancouver:
Hsiao C. Quantum anomalous Hall effect in the Haldane-Rashba system. [Internet] [Thesis]. NSYSU; 2014. [cited 2021 Jan 26].
Available from: http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0610114-201805.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Hsiao C. Quantum anomalous Hall effect in the Haldane-Rashba system. [Thesis]. NSYSU; 2014. Available from: http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0610114-201805
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
NSYSU
22.
Chen, Sung-Ping.
Prediction of Quantum Anomalous Hall Insulator in Functionalized GaBi Honeycomb.
Degree: Master, Physics, 2016, NSYSU
URL: http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0613116-024136
► Using first-principles electronic structure calculations, we predict half-fluorinated GaBi honeycomb under tensile strain to harbor quantum anomalous hall (QAH) insulating phases. A single band inversion…
(more)
▼ Using first-principles electronic structure calculations, we predict half-fluorinated
GaBi honeycomb under tensile strain to harbor
quantum anomalous
hall (QAH) insulating phases. A single band inversion at the Î point
was found in spin-polarized band structure calculations including spin-orbit
coupling effects. In order to confirm topological properties, we evaluated the
Chern number (C) and found C = â1, confirming the presence of a QAH
phase. Moreover, the electronic spectrum of a half-fluorinated GaBi nanoribbon
with zigzag edge is shown to possess only one edge band crossing the
Fermi level within the band gap, which leads insulated state to conductive
state. And last, we discussed halogenated and hydrogenated GaBi and compared
with fluorinated GaBi. Our results suggest that half-functionalized of
the GaBi honeycomb under tensile strain can potentially provide a new platform
for developing novel spintronics devices based on the QAH
phase.
Advisors/Committee Members: Shin-Ming Huang (chair), Feng-Chuan Chuang (committee member), Shi-Hsin Lin (chair), Wan-Sheng Su (chair), Ta-Hsiung Cho (chair).
Subjects/Keywords: First-principles calculations; Band structure; Quantum anomalous Hall effect; Topological phase transition; GaBi honeycomb
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APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Chen, S. (2016). Prediction of Quantum Anomalous Hall Insulator in Functionalized GaBi Honeycomb. (Thesis). NSYSU. Retrieved from http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0613116-024136
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Chen, Sung-Ping. “Prediction of Quantum Anomalous Hall Insulator in Functionalized GaBi Honeycomb.” 2016. Thesis, NSYSU. Accessed January 26, 2021.
http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0613116-024136.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Chen, Sung-Ping. “Prediction of Quantum Anomalous Hall Insulator in Functionalized GaBi Honeycomb.” 2016. Web. 26 Jan 2021.
Vancouver:
Chen S. Prediction of Quantum Anomalous Hall Insulator in Functionalized GaBi Honeycomb. [Internet] [Thesis]. NSYSU; 2016. [cited 2021 Jan 26].
Available from: http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0613116-024136.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Chen S. Prediction of Quantum Anomalous Hall Insulator in Functionalized GaBi Honeycomb. [Thesis]. NSYSU; 2016. Available from: http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0613116-024136
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
University of Michigan
23.
Gu, Jiahua.
Ground-state Overlaps and Topological Phase Transitions.
Degree: PhD, Physics, 2019, University of Michigan
URL: http://hdl.handle.net/2027.42/151491
► For decades, Landau’s theory of phase transition has provided a successful classification for quantum and classical states of matter based on their symmetry broken patterns,…
(more)
▼ For decades, Landau’s theory of
phase transition has provided a successful classification for
quantum and classical states of matter based on their symmetry broken patterns, except for certain exotic
quantum states such as the fractional
quantum Hall (FQH) effect. However, such exotic phenomena are crucial for a complete understanding of the nature. This thesis explores new physical principles emerging from topology and topological states.
First, we use an example to demonstrate Landau’s theory by studying a pair-density wave system, where the symmetry-breaking paradigm is applicable. It turns out that such a system exhibits the Kosterlitz-Thouless (KT)
transition, a
phase transition driven by the proliferation of topological defects, i.e. vortex-antivortex pairs. For topological systems, where symmetry broken pattern cannot be used as a classification tool, we prove a theorem that two gapped systems with non-vanishing ground-state overlap must be adiabatically connected, and thus are necessarily in the same topological
phase. This theorem provides a simple and generic approach to classify topological band insulators/superconductors, without the needs to calculate any known or yet-to-known topological indices. Once the overlap is found nonzero, the two systems must be topologically identical. After presenting a generic proof, the theorem is also verified through calculating the overlap for several milestone topological band insulators and certain interacting systems.
Such an overlap technique is then generalized to (2+1)-D strongly-interacting topological systems at fixed points, including both symmetry-protected topological (SPT) states and intrinsic topological states like FQH. For interacting topological states, the main challenge of utilizing wave-function overlaps to classify them lies in the famous Anderson orthogonality catastrophe (AOC), which states that two different many-body wave functions must have zero overlap in the thermodynamic limit. In this thesis, we found that wave-function overlaps indeed carry critical information about the topological nature of
quantum states and this information can be extracted from the finite-size scaling of the overlaps. In the finite-size scaling analysis, we found a universal topological response term as a sub-leading contribution. This term depends on both the central charge of the corresponding conformal field theory (CFT) and the Euler characteristics of the underlying manifolds on which the system is defined. This term reveals a fundamental connection between ground-state overlaps and CFT’s. In addition, surprisingly, the overlap between an intrinsic topological state and a topologically trivial product state shows a decay faster than the exponential behavior expected via a typical AOC analysis. Such finite-size scaling behaviors could be utilized to theoretically detect the gapless edge modes, and to distinguish the topology of
quantum states or serve as a signature of topological
phase transitions. Possible generalization to higher dimensions and generic…
Advisors/Committee Members: Sun, Kai (committee member), Kurdak, Cagliyan (committee member), Li, Lu (committee member), Liu, James T (committee member).
Subjects/Keywords: condensed matter; topological insulator; SPT; topological order; phase transition; quantum; Physics; Science
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Manager
APA (6th Edition):
Gu, J. (2019). Ground-state Overlaps and Topological Phase Transitions. (Doctoral Dissertation). University of Michigan. Retrieved from http://hdl.handle.net/2027.42/151491
Chicago Manual of Style (16th Edition):
Gu, Jiahua. “Ground-state Overlaps and Topological Phase Transitions.” 2019. Doctoral Dissertation, University of Michigan. Accessed January 26, 2021.
http://hdl.handle.net/2027.42/151491.
MLA Handbook (7th Edition):
Gu, Jiahua. “Ground-state Overlaps and Topological Phase Transitions.” 2019. Web. 26 Jan 2021.
Vancouver:
Gu J. Ground-state Overlaps and Topological Phase Transitions. [Internet] [Doctoral dissertation]. University of Michigan; 2019. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/2027.42/151491.
Council of Science Editors:
Gu J. Ground-state Overlaps and Topological Phase Transitions. [Doctoral Dissertation]. University of Michigan; 2019. Available from: http://hdl.handle.net/2027.42/151491
Leiden University
24.
Rocha, Henrique Bergallo.
Fermion-Boson Dualities in 2+1 Dimensions and Higher.
Degree: 2018, Leiden University
URL: http://hdl.handle.net/1887/64693
► An overview of Quantum Field Theory dualities is given, highlighting the tools physicists have been using to derive them and the importance of symmetries in…
(more)
▼ An overview of
Quantum Field Theory dualities is given, highlighting the tools physicists have been using to derive them and the importance of symmetries in searching for such dualities. Most duality derivations take place in 2+1d where one may use flux attachment to realise dualities between fermionic and bosonic theories. The
phase transition method for finding dualities is then discussed in 2+1d and 3+1d, and a novel derivation of the Montonen-Olive duality is given using this method.
Advisors/Committee Members: Schalm, Koenraad (advisor).
Subjects/Keywords: quantum field theory; topology; duality; bosonization; condensed matter; high energy physics; chern-simons; phase transition
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APA (6th Edition):
Rocha, H. B. (2018). Fermion-Boson Dualities in 2+1 Dimensions and Higher. (Masters Thesis). Leiden University. Retrieved from http://hdl.handle.net/1887/64693
Chicago Manual of Style (16th Edition):
Rocha, Henrique Bergallo. “Fermion-Boson Dualities in 2+1 Dimensions and Higher.” 2018. Masters Thesis, Leiden University. Accessed January 26, 2021.
http://hdl.handle.net/1887/64693.
MLA Handbook (7th Edition):
Rocha, Henrique Bergallo. “Fermion-Boson Dualities in 2+1 Dimensions and Higher.” 2018. Web. 26 Jan 2021.
Vancouver:
Rocha HB. Fermion-Boson Dualities in 2+1 Dimensions and Higher. [Internet] [Masters thesis]. Leiden University; 2018. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/1887/64693.
Council of Science Editors:
Rocha HB. Fermion-Boson Dualities in 2+1 Dimensions and Higher. [Masters Thesis]. Leiden University; 2018. Available from: http://hdl.handle.net/1887/64693
University of Minnesota
25.
Leng, Xiang.
Superconductor-insulator transition induced by electrostatic charging in high temperature superconductors.
Degree: PhD, Physics, 2011, University of Minnesota
URL: http://purl.umn.edu/119343
► Ultrathin YBa2Cu3O7−x films were grown on SrTiO3 substrates in a high pressure oxygen sputtering system to study the superconductor-insulator transition by electrostatic charging. While backside…
(more)
▼ Ultrathin YBa2Cu3O7−x films were grown on SrTiO3 substrates in a high pressure
oxygen sputtering system to study the superconductor-insulator transition by
electrostatic charging. While backside gating using SrTiO3 as a dielectric induces
only small TC shifts, a clear transition between superconducting and insulating behavior
was realized in a 7 unit cell thick film using an ionic liquid as the dielectric.
Employing a finite size scaling analysis, curves of resistance versus temperature,
R(T), over the temperature range from 6 K to 22 K were found to collapse onto
a single function, which suggests the presence of a quantum critical point. However
the scaling failed at the lowest temperatures indicating the possible presence
of an additional phase between the superconducting and insulating regimes. In
the presence of magnetic field, a cleaner superconductor-insulator transition was
realized by electrostatic charging. A scaling analysis showed that this was a quantum
phase transition. The magnetic field did not change the universality class.
Further depletion of holes caused electrons to be accumulated in the film and the
superconductivity to be recovered. This could be an n-type superconductor. The
carriers were found to be highly localized.
By changing the polarity of the gate voltage, an underdoped 7 unit cell thick
film was tuned into the overdoped regime. This process proved to be reversible.
Transport measurements showed a series of anomalous features compared to chemically
doped bulk samples and an unexpected two-step mechanism for electrostatic
doping was revealed. These anomalous behaviors suggest that there is an electronic
phase transition in the Fermi surface around the optimal doping level.
Subjects/Keywords: High Tc superconducotor; Ionic liquid; Quantum Phase Transition; Superconductor Insulator tanstion; Physics
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APA (6th Edition):
Leng, X. (2011). Superconductor-insulator transition induced by electrostatic charging in high temperature superconductors. (Doctoral Dissertation). University of Minnesota. Retrieved from http://purl.umn.edu/119343
Chicago Manual of Style (16th Edition):
Leng, Xiang. “Superconductor-insulator transition induced by electrostatic charging in high temperature superconductors.” 2011. Doctoral Dissertation, University of Minnesota. Accessed January 26, 2021.
http://purl.umn.edu/119343.
MLA Handbook (7th Edition):
Leng, Xiang. “Superconductor-insulator transition induced by electrostatic charging in high temperature superconductors.” 2011. Web. 26 Jan 2021.
Vancouver:
Leng X. Superconductor-insulator transition induced by electrostatic charging in high temperature superconductors. [Internet] [Doctoral dissertation]. University of Minnesota; 2011. [cited 2021 Jan 26].
Available from: http://purl.umn.edu/119343.
Council of Science Editors:
Leng X. Superconductor-insulator transition induced by electrostatic charging in high temperature superconductors. [Doctoral Dissertation]. University of Minnesota; 2011. Available from: http://purl.umn.edu/119343
University of Waterloo
26.
Schulz-Beach, Jonathon Matthew.
Explorations in machine learning for interacting many-body systems.
Degree: 2020, University of Waterloo
URL: http://hdl.handle.net/10012/16239
► Most interacting many-body systems in physics are not analytically solvable. Instead, numerical methods are needed for the study of these complex and high-dimensional problems. At…
(more)
▼ Most interacting many-body systems in physics are not analytically solvable. Instead, numerical methods are needed for the study of these complex and high-dimensional problems. At present, there are many interesting problems in strongly correlated systems that remain unsolved with current methods. At the heart of this problem is finding an efficient representation that incorporates symmetries, correlations and general features.
In the context of computer science, machine learning techniques have had astonishing success at reducing the dimensionality of data. The leading method is through the use of artificial neural networks. These networks have been enormously successful at sifting through vast amounts of data to find patterns and regularities. In a sense, neural networks are themselves a statistical system whose properties are adjusted to mimic the features of the data. By finding an effective low-dimensional representation of the data, machine learning has greatly subdued the curse of dimensionality found in many real-world problems.
In this Thesis, we apply several machine learning techniques to the study of interacting many-body systems in classical and quantum statistical physics. We explore supervised classification of phases of matter with an emphasis on physical interpretation of the net- work. In doing so, we design a custom network architecture that possesses rotational symmetry as an inductive bias. We further investigate connections between the renormalization group and deep learning through applying a super-resolving neural network to the classical Ising model. Towards experimental efforts, we also repurpose generative machine learning to quantum state tomography for the calibration and testing of quantum devices. We conclude with a latent variable model inspired by near-term quantum algorithms. This maps to a variational Monte Carlo ansatz that produces samples efficiently for interacting quantum systems.
Subjects/Keywords: machine learning; condensed matter; physics; statistical physics; neural network; monte carlo; phase transition; quantum computing
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CSE |
Export
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APA (6th Edition):
Schulz-Beach, J. M. (2020). Explorations in machine learning for interacting many-body systems. (Thesis). University of Waterloo. Retrieved from http://hdl.handle.net/10012/16239
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Schulz-Beach, Jonathon Matthew. “Explorations in machine learning for interacting many-body systems.” 2020. Thesis, University of Waterloo. Accessed January 26, 2021.
http://hdl.handle.net/10012/16239.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Schulz-Beach, Jonathon Matthew. “Explorations in machine learning for interacting many-body systems.” 2020. Web. 26 Jan 2021.
Vancouver:
Schulz-Beach JM. Explorations in machine learning for interacting many-body systems. [Internet] [Thesis]. University of Waterloo; 2020. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/10012/16239.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Schulz-Beach JM. Explorations in machine learning for interacting many-body systems. [Thesis]. University of Waterloo; 2020. Available from: http://hdl.handle.net/10012/16239
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
University of Sydney
27.
Manning, Adrian Gordon.
Quantum Fields in Curved Spacetime with Cosmological and Gravitational Wave Implications
.
Degree: 2018, University of Sydney
URL: http://hdl.handle.net/2123/17804
► A range of novel ideas, covering both general relativity and quantum field theory are introduced and explored. An analytic procedure for theories that modify the…
(more)
▼ A range of novel ideas, covering both general relativity and quantum field theory are introduced and explored. An analytic procedure for theories that modify the stress-energy-tensor in general relativity is examined which compares predicted deviations in the gravitational wave radiation from binary black hole mergers to the observed waveform from recent detections, i.e GW150914. This is applied directly to the theory of non-commutative spacetimes, which ultimately constrains the scale of non-commutative spacetime up to the Planck scale, some 15 orders of magnitude improvement on previous bounds. The stochastic background of gravitational wave radiation from first order electroweak phase transitions in the early universe is also examined. This is done in the context of the non-linearly realised electroweak sector of the Standard Model, which allows for a direct relation between coupling constants of the model and parameters of the expected stochastic gravitational wave background. For this particular model, a range of values are shown to not only produce gravitational waves detectable by future space-based detectors, such as eLISA, but can potentially create low-frequency radiation detectable by pulsar timing array experiments, such as the future SKA. Finally, non-inertial effects in the context of quantum fields in curved spacetimes are examined for a number of metrics. An oscillatory motion in the velocity expectation of a single fermionic particle is shown to exist in cosmological/expanding spacetimes, but not for accelerating or rotating spacetimes. In the rotating case, a new quantisation scheme is introduced along with the Bogoliubov coefficients enabling general calculations in rotating spaces to be computed with respect to defined non-rotating fermionic particle states.
Subjects/Keywords: gravitational waves;
electroweak phase transition;
baryogenesis;
curved spacetime;
fermions;
quantum field theory
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APA (6th Edition):
Manning, A. G. (2018). Quantum Fields in Curved Spacetime with Cosmological and Gravitational Wave Implications
. (Thesis). University of Sydney. Retrieved from http://hdl.handle.net/2123/17804
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Manning, Adrian Gordon. “Quantum Fields in Curved Spacetime with Cosmological and Gravitational Wave Implications
.” 2018. Thesis, University of Sydney. Accessed January 26, 2021.
http://hdl.handle.net/2123/17804.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Manning, Adrian Gordon. “Quantum Fields in Curved Spacetime with Cosmological and Gravitational Wave Implications
.” 2018. Web. 26 Jan 2021.
Vancouver:
Manning AG. Quantum Fields in Curved Spacetime with Cosmological and Gravitational Wave Implications
. [Internet] [Thesis]. University of Sydney; 2018. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/2123/17804.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Manning AG. Quantum Fields in Curved Spacetime with Cosmological and Gravitational Wave Implications
. [Thesis]. University of Sydney; 2018. Available from: http://hdl.handle.net/2123/17804
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Purdue University
28.
Thomas, Brianna S. Dillon.
Localization and delocalization in two-dimensional quantum percolation.
Degree: PhD, Physics & Astronomy, 2016, Purdue University
URL: https://docs.lib.purdue.edu/open_access_dissertations/864
► Quantum percolation is one of several disorder-only models that address the question of whether conduction, or more generally, delocalization, is possible in two dimensional…
(more)
▼ Quantum percolation is one of several disorder-only models that address the question of whether conduction, or more generally, delocalization, is possible in two dimensional disordered systems. Whether
quantum percolation exhibits a delocalization-localization
phase transition in two dimensions is an ongoing debate, but many recent studies point toward there being a delocalized
phase at non-zero disorder, in contradiction to the behavior of the Anderson model, another disorder-only model. In this dissertation, I present my research on
quantum percolation that shows a delocalized state is possible, both on isotropic lattices and on highly anisotropic lattices, and shows that the essential characteristics of the
quantum percolation model are maintained even when the model is modified to allow tunneling through diluted sites. In Chapter 1, I provide an overview of the scaling theory for the Anderson model, the history of the
quantum percolation model, and the computational methods used to study the
quantum percolation model in two dimensions. In Chapter 2, I study the two-dimensional
quantum percolation model with site percolation on isotropic square lattices using numerical calculations of the transmission coefficient
T on a much larger scale and over a much wider range of parameters than was done previously. I confirm the existence of delocalized, power-law localized, and exponentially localized phases, and determine a detailed, quantitative
phase diagram for energies 0.001 ≤ E ≤ 1.6 and dilutions 2% ≤
q ≤ 38%. Additionally, I show that the delocalized
phase is not merely a finite size effect. In Chapter 3, I examine the same 2D
quantum percolation model on highly anisotropic strips of varying width, to investigate why the isotropic lattice results show a delocalized
phase, unlike work by others on anisotropic strips, in particular that of Soukoulis and Grest [Phys. Rev. B 44, 4685 (1991)] using the transfer matrix method . The model is studied over a dilution range extending to lower dilutions than those studied by Soukoulis and Grest, and I find evidence of a delocalized
phase at these low dilutions, with
phase boundaries that agree with my previous work. In Chapter 4, I modify the 2D
quantum percolation model to allow for tunneling through and between diluted sites by making the hopping integral for diluted sites be a non-zero fraction of the hopping integral for occupied sites, while yet maintaining a binary disorder. Using numerical calculations of the transmission coefficient
T as in Chapter 1, I determine a complete, detailed three-parameter
phase diagram showing the effects of energy
E, dilution
q, and hopping integral
w. I find that the three phases characteristic of
quantum percolation persist for a fairly large range of
w before the entire system becomes delocalized at sufficiently large
w. Additionally, I examine the inverse participation ratio (IPR) to gain a complementary picture of how the particle’s wave function changes with…
Advisors/Committee Members: Hisao Nakanishi, Hisao Nakanishi, Erica Carlson, Andrew S. Hirsch, Sabre Kais.
Subjects/Keywords: Pure sciences; 2-dimensional systems; Localization; Percolation; Phase transition; Quantum transport; Condensed Matter Physics
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Manager
APA (6th Edition):
Thomas, B. S. D. (2016). Localization and delocalization in two-dimensional quantum percolation. (Doctoral Dissertation). Purdue University. Retrieved from https://docs.lib.purdue.edu/open_access_dissertations/864
Chicago Manual of Style (16th Edition):
Thomas, Brianna S Dillon. “Localization and delocalization in two-dimensional quantum percolation.” 2016. Doctoral Dissertation, Purdue University. Accessed January 26, 2021.
https://docs.lib.purdue.edu/open_access_dissertations/864.
MLA Handbook (7th Edition):
Thomas, Brianna S Dillon. “Localization and delocalization in two-dimensional quantum percolation.” 2016. Web. 26 Jan 2021.
Vancouver:
Thomas BSD. Localization and delocalization in two-dimensional quantum percolation. [Internet] [Doctoral dissertation]. Purdue University; 2016. [cited 2021 Jan 26].
Available from: https://docs.lib.purdue.edu/open_access_dissertations/864.
Council of Science Editors:
Thomas BSD. Localization and delocalization in two-dimensional quantum percolation. [Doctoral Dissertation]. Purdue University; 2016. Available from: https://docs.lib.purdue.edu/open_access_dissertations/864
Western Michigan University
29.
Li, Chengyang.
Studies of the Quantum Phase Transition in Chromium Using Inelastic X-Ray Scattering and Ab Initio Methods.
Degree: PhD, Physics, 2014, Western Michigan University
URL: https://scholarworks.wmich.edu/dissertations/284
► In this project, inelastic x-ray scattering (IXS) was used to measure the phonon dispersion in chromium at high pressure and low temperature, and an…
(more)
▼ In this project, inelastic x-ray scattering (IXS) was used to measure the phonon dispersion in chromium at high pressure and low temperature, and an ab initio method was used to simulate the phonon dispersion with different lattice constants and magnetic orders. The IXS measurements were carried out in Sector 30 at the Advanced Photon Source at Argonne National Laboratory. Data were taken at room temperature with pressures of 1.29 GPa, 8.15 GPa, 10.6 GPa, and at 5 K with a pressure of 18.36 GPa. The data shows similar phonon behavior in the antiferromagnetism (AFM) and the spin density wave (SDW) states at room temperature, but different phonon behavior at 5 K and 18.6 GPa. The ab initio simulation was used to calculate the phonon dispersion with AFM plus SDW at the lattice constant corresponding to the measured pressure in the experiment. By comparing the experimental data and the simulation result, it seems likely that a new state exists after the
quantum phase transition.
Advisors/Committee Members: Dr. Clement Burns, Dr. Arthur McGurn, Dr. Thomas Gorczyca.
Subjects/Keywords: Quantum phase transition; ab initio method; x-ray scattering; high resolution; high pressure; quantum ESPRESSO; Physics
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APA ·
Chicago ·
MLA ·
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Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Li, C. (2014). Studies of the Quantum Phase Transition in Chromium Using Inelastic X-Ray Scattering and Ab Initio Methods. (Doctoral Dissertation). Western Michigan University. Retrieved from https://scholarworks.wmich.edu/dissertations/284
Chicago Manual of Style (16th Edition):
Li, Chengyang. “Studies of the Quantum Phase Transition in Chromium Using Inelastic X-Ray Scattering and Ab Initio Methods.” 2014. Doctoral Dissertation, Western Michigan University. Accessed January 26, 2021.
https://scholarworks.wmich.edu/dissertations/284.
MLA Handbook (7th Edition):
Li, Chengyang. “Studies of the Quantum Phase Transition in Chromium Using Inelastic X-Ray Scattering and Ab Initio Methods.” 2014. Web. 26 Jan 2021.
Vancouver:
Li C. Studies of the Quantum Phase Transition in Chromium Using Inelastic X-Ray Scattering and Ab Initio Methods. [Internet] [Doctoral dissertation]. Western Michigan University; 2014. [cited 2021 Jan 26].
Available from: https://scholarworks.wmich.edu/dissertations/284.
Council of Science Editors:
Li C. Studies of the Quantum Phase Transition in Chromium Using Inelastic X-Ray Scattering and Ab Initio Methods. [Doctoral Dissertation]. Western Michigan University; 2014. Available from: https://scholarworks.wmich.edu/dissertations/284
Duke University
30.
Mebrahtu, Henok Tesfamariam.
Electron Transport through Carbon Nanotube Quantum Dots in A Dissipative Environment
.
Degree: 2012, Duke University
URL: http://hdl.handle.net/10161/5487
► The role of the surroundings, or environment , is essential in understanding funda- mental quantum-mechanical concepts, such as quantum measurement and quantum entanglement. It…
(more)
▼ The role of the surroundings, or environment , is essential in understanding funda- mental
quantum-mechanical concepts, such as
quantum measurement and
quantum entanglement. It is thought that a dissipative environment may be responsible for certain types of
quantum (i.e. zero-temperature)
phase transitions. We observe such a
quantum phase transition in a very basic system: a resonant level coupled to a dissipative environment. Specifically, the resonant level is formed by a quantized state in a carbon nanotube, and the dissipative environment is realized in resistive leads; and we study the shape of the resonant peak by measuring the nanotube electronic conductance. In sequential tunneling regime, we find the height of the single-electron conductance peaks increases as the temperature is lowered, although it scales more weakly than the conventional T
-1. Moreover, the observed scaling signals a close connec- tion between fluctuations that influence tunneling phenomenon and macroscopic models of the electromagnetic environment. In the resonant tunneling regime (temperature smaller than the intrinsic level width), we characterize the resonant conductance peak, with the expectation that the width and height of the resonant peak, both dependent on the tunneling rate, will be suppressed. The observed behavior crucially depends on the ratio of the coupling between the resonant level and the two contacts. In asymmetric barriers the peak width approaches saturation, while the peak height starts to decrease. Overall, the peak height shows a non-monotonic temperature dependence. In sym- metric barriers case, the peak width shrinks and we find a regime where the unitary conductance limit is reached in the incoherent resonant tunneling. We interpret this behavior as a manifestation of a
quantum phase transition. Finally, our setup emulates tunneling in a Luttinger liquid (LL), an interacting one-dimensional electron system, that is distinct from the conventional Fermi liquids formed by electrons in two and three dimensions. Some of the most spectacular properties of LL are revealed in the process of electron tunneling: as a function of the applied bias or temperature the tunneling current demonstrates a non-trivial power-law suppression. Our setup allows us to address many prediction of resonant tunneling in a LL, which have not been experimentally tested yet.
Advisors/Committee Members: Finkelstein, Gleb (advisor).
Subjects/Keywords: Physics;
Condensed matter physics;
Nanoscience;
carbon nanotube;
dissipation;
luttinger liquid;
quantum dot;
quantum phase transition;
resonant tunneling
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Manager
APA (6th Edition):
Mebrahtu, H. T. (2012). Electron Transport through Carbon Nanotube Quantum Dots in A Dissipative Environment
. (Thesis). Duke University. Retrieved from http://hdl.handle.net/10161/5487
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Mebrahtu, Henok Tesfamariam. “Electron Transport through Carbon Nanotube Quantum Dots in A Dissipative Environment
.” 2012. Thesis, Duke University. Accessed January 26, 2021.
http://hdl.handle.net/10161/5487.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Mebrahtu, Henok Tesfamariam. “Electron Transport through Carbon Nanotube Quantum Dots in A Dissipative Environment
.” 2012. Web. 26 Jan 2021.
Vancouver:
Mebrahtu HT. Electron Transport through Carbon Nanotube Quantum Dots in A Dissipative Environment
. [Internet] [Thesis]. Duke University; 2012. [cited 2021 Jan 26].
Available from: http://hdl.handle.net/10161/5487.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Mebrahtu HT. Electron Transport through Carbon Nanotube Quantum Dots in A Dissipative Environment
. [Thesis]. Duke University; 2012. Available from: http://hdl.handle.net/10161/5487
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
◁ [1] [2] [3] [4] ▶
. 
Open Access Theses and Dissertations
