+publisher:"Brown University" +contributor:("Mitrovic, Vesna")

1. Zou, Xiaojing. Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures.

Degree: PhD, Physics, 2009, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:233/

► We have fabricated and investigated the electrical and magnetic behavior of polycrystalline and epitaxial CrO2 nanostructures, grown using selective-area growth technique. Magnetic domain structures were… (more)

▼ We have fabricated and investigated the electrical and magnetic behavior of polycrystalline and epitaxial CrO2 nanostructures, grown using selective-area growth technique. Magnetic domain structures were studied by magnetic force microscopy, and in-plane, lamellar domain structure with fragmented walls aligned along the magnetic easy axis direction have been observed, indicating a large magnetocrystalline anisotropy in epitaxial CrO2 nanostructures. Low-temperature transport measurements on nanowires have shown that the dc resistivity of polycrystalline CrO2 wires is strongly dependent on the linewidth. Below a critical temperature, a transition from a positive to a negative temperature coefficient of resistivity have been observed, which we attribute to a competition between the scattering of the conduction electrons inside the grains and scattering across the grain boundaries. Using a model based on grain boundary scattering, we estimate a mean transmission probability through the grain boundaries to be on the order of 10?1. Furthermore, magnetoresistance (MR) measurement indicates that the MR behavior of polycrystalline wires is dominated by the shape anisotropy; however, for epitaxial wires, both the shape and magnetocrystalline anisotropy play important roles, and the resulting MR properties are found to be closely related to the orientation of the wire axis. By studying the MR curves, we inferred the internal domain structures in various single crystal CrO2 wires and found that the spin-dependent transport is much stronger across a grain boundary than a domain wall. We have also studied the magnetotransport properties of CrO2 nanocontacts. Manipulating the domain walls using a large dc current in the contact area yields a magnetoresistance of up to 25%, which is the largest ever seen in a single ferromagnetic film. The single domain-wall-resistance is determined to be three orders of magnitude larger than that of conventional 3d ferromagnets, as a result of the material's half-metallicity. We have measured DWR and the spin-torque effect along different crystallographic axes and at varying temperatures. Finally, we present the results of a theoretical analysis of this system, based on its half-metallic character and on the intrinsic magnetic behavior of CrO2. Advisors/Committee Members: Xiao, Gang (director), Sun, Shouheng (reader), Mitrovic, Vesna (reader).

Subjects/Keywords: Chromium Dioxide

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APA (6^th Edition):

Zou, X. (2009). Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:233/

Chicago Manual of Style (16^th Edition):

Zou, Xiaojing. “Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures.” 2009. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:233/.

MLA Handbook (7^th Edition):

Zou, Xiaojing. “Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures.” 2009. Web. 05 Dec 2020.

Vancouver:

Zou X. Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures. [Internet] [Doctoral dissertation]. Brown University; 2009. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:233/.

Council of Science Editors:

Zou X. Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures. [Doctoral Dissertation]. Brown University; 2009. Available from: https://repository.library.brown.edu/studio/item/bdr:233/

2. Zucker, Philip Thomas. Novel Probes of Topological Order in the Quantum Hall Effect.

Degree: Department of Physics, 2017, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:733585/

► The quantum Hall effect is a marvelous thing, a microcosm of all that is strange and beautiful and quantum. The fractional quantum Hall effect supports… (more)

▼ The quantum Hall effect is a marvelous thing, a microcosm of all that is strange and beautiful and quantum. The fractional quantum Hall effect supports quasiparticles of fractional charge and exotic statistics. These systems are not just a theorist's fancy and are measurable in lab. Even for properties that are still waiting for conclusive experimental confirmation, we have strong theoretical reasons to assume their existence, giving something for experimentalists to strive for as well. After nearly 40 years, the field isn't closed and can still yield surprises. In this thesis, a number of novel probes of the nature of the topological order existing in these systems are discussed, in particular focussing on the mystery of the ν=5/2 filling factor. Because of the bulk gap, low energy physics in the quantum Hall effect is confined to the edges of the 2D electron liquid. The velocities of edge modes are key parameters of edge physics. They were determined in several quantum Hall systems from time-resolved measurements and high-frequency ac transport. A way is proposed to extract edge velocities from dc transport in a point contact geometry defined by narrow gates. The width of the gates assumes two different sizes at small and large distances from the point contact. The Coulomb interaction across the gates depends on the gate width and affects the conductance of the contact. The conductance exhibits two different temperature dependencies at high and low temperatures. The transition between the two regimes is determined by the edge velocity. An interesting feature of the low-temperature I-V curve is current oscillations as a function of the voltage. The oscillations emerge due to charge reflection from the interface of the regions defined by the narrow and wide sections of the gates. Numerical results suggest that the quantum Hall effect at ν=5/2 is described by the Pfaffian or anti-Pfaffian state in the absence of disorder and Landau level mixing. Those states are incompatible with the observed transport properties of GaAs heterostructures, where disorder and Landau level mixing are strong. We show that the recent proposal of a PH-Pfaffian topological order by Son is consistent with all experiments. The absence of the particle-hole symmetry at ν=5/2 is not an obstacle to the existence of the PH-Pfaffian order since the order is robust to symmetry breaking. Advisors/Committee Members: Feldman, Dmitri (Advisor), Mitrovic, Vesna (Reader), Valles, James (Reader).

Subjects/Keywords: Quantum Hall effect

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APA (6^th Edition):

Zucker, P. T. (2017). Novel Probes of Topological Order in the Quantum Hall Effect. (Thesis). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:733585/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Zucker, Philip Thomas. “Novel Probes of Topological Order in the Quantum Hall Effect.” 2017. Thesis, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:733585/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Zucker, Philip Thomas. “Novel Probes of Topological Order in the Quantum Hall Effect.” 2017. Web. 05 Dec 2020.

Vancouver:

Zucker PT. Novel Probes of Topological Order in the Quantum Hall Effect. [Internet] [Thesis]. Brown University; 2017. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:733585/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Zucker PT. Novel Probes of Topological Order in the Quantum Hall Effect. [Thesis]. Brown University; 2017. Available from: https://repository.library.brown.edu/studio/item/bdr:733585/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

3. Lu, Lu. Nuclear Magnetic Resonance Study of Ferromagnetism and Local Symmetry Breaking in Double Perovskite Mott Insulator Ba2NaOsO6.

Degree: PhD, Physics, 2015, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:674146/

► Study of the combined effects of strong electronic correlations with spin-orbit coupling (SOC) represents a central issue in quantum materials research. Predicting emergent properties represents… (more)

Subjects/Keywords: NMR

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APA (6^th Edition):

Lu, L. (2015). Nuclear Magnetic Resonance Study of Ferromagnetism and Local Symmetry Breaking in Double Perovskite Mott Insulator Ba2NaOsO6. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:674146/

Chicago Manual of Style (16^th Edition):

Lu, Lu. “Nuclear Magnetic Resonance Study of Ferromagnetism and Local Symmetry Breaking in Double Perovskite Mott Insulator Ba2NaOsO6.” 2015. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:674146/.

MLA Handbook (7^th Edition):

Lu, Lu. “Nuclear Magnetic Resonance Study of Ferromagnetism and Local Symmetry Breaking in Double Perovskite Mott Insulator Ba2NaOsO6.” 2015. Web. 05 Dec 2020.

Vancouver:

Lu L. Nuclear Magnetic Resonance Study of Ferromagnetism and Local Symmetry Breaking in Double Perovskite Mott Insulator Ba2NaOsO6. [Internet] [Doctoral dissertation]. Brown University; 2015. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:674146/.

Council of Science Editors:

Lu L. Nuclear Magnetic Resonance Study of Ferromagnetism and Local Symmetry Breaking in Double Perovskite Mott Insulator Ba2NaOsO6. [Doctoral Dissertation]. Brown University; 2015. Available from: https://repository.library.brown.edu/studio/item/bdr:674146/

4. Joy, James Charles. Studies of the Bose Insulator to Fermi Insulator Crossover Near the Two-Dimensional Superconductor-Insulator Transition.

Degree: Department of Physics, 2017, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:733372/

► Experiments have established the existence of a Bose Insulator phase close to the two dimensional Superconductor-Insulator transition. Here, current is carried by localized Cooper Pairs,… (more)

▼ Experiments have established the existence of a Bose Insulator phase close to the two dimensional Superconductor-Insulator transition. Here, current is carried by localized Cooper Pairs, which are usually responsible for superconductivity. Several systems show a unified picture of this phase, where Cooper Pairs themselves behave as individual bosons. However, the limits of the region of phase space that it occupies are poorly understood, and there has been limited work examining whether or not pairs survive in the limit of strong disorder. To address this question, we conducted experiments with films grown on nanostructured templates made of Anodic Aluminum Oxide (AAO). We are able to study the influence of both material and topographical properties of thin films on localization in both the bosonic and fermionic regimes. I will detail two studies examining the breadth of these regimes. In the first, finite size effects on systems of weakly coupled superconducting islands are studied by growing films on AAO substrates with small hole spacings. Some experiments show evidence of a substantial shrinking of the bose insulator phase, while others are more ambiguous. We speculate that the degree of inhomogeneity present in the substrates leads to more robust pairing in some films, enhancing the bose insulator phase relative to others. In the second approach, I study scaling of the high temperature resistance, where Cooper pairs are not expected. Since scaling is observed across many fermionic systems, deviations from it can be used as a probe to detect Cooper pairs. Our results show bosons present in the strongly localized regime, where transport is fermionic. I also detail numerical studies of the influence of inhomogeneity on scaling. The simulations show that uniform disorder does not substantially impact the results of scaling, but correlated inhomogeneities can have a drastic impact on the experimental results. Advisors/Committee Members: Valles, James (Advisor), Feldman, Dmitri (Reader), Mitrovic, Vesna (Reader).

Subjects/Keywords: Physics

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APA (6^th Edition):

Joy, J. C. (2017). Studies of the Bose Insulator to Fermi Insulator Crossover Near the Two-Dimensional Superconductor-Insulator Transition. (Thesis). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:733372/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Joy, James Charles. “Studies of the Bose Insulator to Fermi Insulator Crossover Near the Two-Dimensional Superconductor-Insulator Transition.” 2017. Thesis, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:733372/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Joy, James Charles. “Studies of the Bose Insulator to Fermi Insulator Crossover Near the Two-Dimensional Superconductor-Insulator Transition.” 2017. Web. 05 Dec 2020.

Vancouver:

Joy JC. Studies of the Bose Insulator to Fermi Insulator Crossover Near the Two-Dimensional Superconductor-Insulator Transition. [Internet] [Thesis]. Brown University; 2017. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:733372/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Joy JC. Studies of the Bose Insulator to Fermi Insulator Crossover Near the Two-Dimensional Superconductor-Insulator Transition. [Thesis]. Brown University; 2017. Available from: https://repository.library.brown.edu/studio/item/bdr:733372/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

5. Oller, Declan Danesh. Anodic alumina as a scalable platform for structural coloration and optical rectification.

Degree: Department of Physics, 2017, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:792623/

► Anodized aluminum oxide (AAO) is an interesting material, occupying a unique space – already used incredibly widely in the world, yet also commonly used for… (more)

▼ Anodized aluminum oxide (AAO) is an interesting material, occupying a unique space – already used incredibly widely in the world, yet also commonly used for nanoscience research. However, the wealth of scientific research using it has yet to make it to the real world. Similarly, many nanoscience fields that have produced incredible results on a small scale haven’t found practical use. In this dissertation, we investigate scalable applications of AAO in two fields, and then look at their potential intersection. First, we look at its use as a scalable structural coloration platform, employing a Fabry-Perot optical cavity structure that has seen a research resurgence in recent years. Structural coloration presents the potential for a more tunable, durable, and environmentally friendly coloration system than traditional methods, though it can also be used in concert with them. We present tools to analyze the full capabilities of this structure for its future use in structural coloration as a “color by design” platform and verify them with experimental probes of fabricated samples. Further, we look to mitigate assumed limitations of this system, such as sensitivity to fabrication parameters and angular dependence. Then, we present another achievement of AAO as a scalable platform: the dielectric of a Ag-AAO-Al resistive switching (RS) system used for optical rectification (OR). RS is a well researched field, but almost entirely in the electronic context, being the first realization of the memristor. OR is a promising field with potential for energy harvesting and ultrafast light sensing that has seen a resurgence in recent years, but all published methods are either highly unrepeatable or rely on advanced nanofabrication techniques. We demonstrate an intersection of the RS field, used to create a unique OR platform that offers scalability and tunability beyond any that have been reported. We investigate the electronic effects, temperature dependence, and then present possible OR effects. Lastly, we present some potential combinations of these two projects. Advisors/Committee Members: Xu, Jimmy (Advisor), Valles, James (Reader), Mitrovic, Vesna (Reader).

Subjects/Keywords: Optics

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APA (6^th Edition):

Oller, D. D. (2017). Anodic alumina as a scalable platform for structural coloration and optical rectification. (Thesis). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:792623/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Oller, Declan Danesh. “Anodic alumina as a scalable platform for structural coloration and optical rectification.” 2017. Thesis, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:792623/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Oller, Declan Danesh. “Anodic alumina as a scalable platform for structural coloration and optical rectification.” 2017. Web. 05 Dec 2020.

Vancouver:

Oller DD. Anodic alumina as a scalable platform for structural coloration and optical rectification. [Internet] [Thesis]. Brown University; 2017. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:792623/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Oller DD. Anodic alumina as a scalable platform for structural coloration and optical rectification. [Thesis]. Brown University; 2017. Available from: https://repository.library.brown.edu/studio/item/bdr:792623/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

6. Vachon, Marc-Andre. Nuclear Magnetic Resonance Study of the Magnetism in the 2D Frustrated Quantum Heisenberg Antiferromagnet Cs2CuCl4.

Degree: PhD, Physics, 2009, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:93/

► The experimental realization of a two dimensional quantum spin liquid has been eagerly sought since first proposed by Anderson in 1973. Recently, Cs2CuCl4, a frustrated… (more)

▼ The experimental realization of a two dimensional quantum spin liquid has been eagerly sought since first proposed by Anderson in 1973. Recently, Cs2CuCl4, a frustrated 2D quantum antiferromagnet (QAF), has shown potential in this regard triggering immense interest, both experimentally and theoretically. Amongst these studies, different scenarios on the nature of the spin liquid phase were proposed and the presence of exotic magnetic phases in the ground state was noticed. To this date, many of these phases are still obscured and the nature of the spin liquid state remains unsettled. To investigate the above, we present 133Cs Nuclear Magnetic Resonance (NMR)measurements on Cs2CuCl4 at temperature down to 50mK and applied magnetic field up to 15 T. We first demonstrate that Cs NMR is an effective probe of the magnetism in the compound through experiments in the paramagnetic phase. Lower temperature NMR measurements as a function of the strength and orientation of the applied magnetic field provide the most complete picture of the different phases stabilized in Cs2CuCl4. The magnetic character of these phases is discussed in the context of the interplay between quantum fuctuations, frustration and the Dzyaloshinskii-Moriya (DM) interaction. Furthermore, we find evidence of three new phase transitions, as well as an unexpected angular dependence of the saturation field. These findings suggest that the accepted Hamiltonian requires modifications, such as additional DM interactions. In order to probe the nature of the spin liquid state, local magnetization and spin-lattice relaxation rate measurements were performed. A comparison with the result of a variational calculation using Gutzwiller-projected mean-field theory demonstrates the 2D magnetic behavior of the local magnetization. In addition, both temperature and magnetic field dependence of the spin-lattice relaxation rate suggests that the relevant low energy quasiparticle excitations obey fermionic statistics. Advisors/Committee Members: Mitrovic, Vesna (director), Marston, J. (reader), Valles, James (reader).

Subjects/Keywords: NMR

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APA (6^th Edition):

Vachon, M. (2009). Nuclear Magnetic Resonance Study of the Magnetism in the 2D Frustrated Quantum Heisenberg Antiferromagnet Cs2CuCl4. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:93/

Chicago Manual of Style (16^th Edition):

Vachon, Marc-Andre. “Nuclear Magnetic Resonance Study of the Magnetism in the 2D Frustrated Quantum Heisenberg Antiferromagnet Cs2CuCl4.” 2009. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:93/.

MLA Handbook (7^th Edition):

Vachon, Marc-Andre. “Nuclear Magnetic Resonance Study of the Magnetism in the 2D Frustrated Quantum Heisenberg Antiferromagnet Cs2CuCl4.” 2009. Web. 05 Dec 2020.

Vancouver:

Vachon M. Nuclear Magnetic Resonance Study of the Magnetism in the 2D Frustrated Quantum Heisenberg Antiferromagnet Cs2CuCl4. [Internet] [Doctoral dissertation]. Brown University; 2009. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:93/.

Council of Science Editors:

Vachon M. Nuclear Magnetic Resonance Study of the Magnetism in the 2D Frustrated Quantum Heisenberg Antiferromagnet Cs2CuCl4. [Doctoral Dissertation]. Brown University; 2009. Available from: https://repository.library.brown.edu/studio/item/bdr:93/

7. Wang, Chenjie. Transport in Quantum Hall Systems: Probing Anyons and Edge Physics.

Degree: PhD, Physics, 2012, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:297718/

► Several aspects of transport in fractional quantum Hall (FQH) systems are investigated. The focus is on the FQH system at filling factor 5/2, which is… (more)

▼ Several aspects of transport in fractional quantum Hall (FQH) systems are investigated. The focus is on the FQH system at filling factor 5/2, which is expected to host non-Abelian anyons. We study interferometry signatures of the anyonic statistics in the 5/2 state. It has been shown that non-Abelian states and the Abelian 331 states may have identical signatures in Fabry-Perot interferometry in the 5/2 FQH system. We study a Mach-Zehnder interferometer and demonstrate that current and shot noise measurements are able to distinguish the 331 states from the non-Abelian counterparts. We find that the flux-dependent Fano factor has the maximal value of 2*1.4e for the 331 state with flavor symmetry. Without such symmetry, the Fano factor can reach 2*2.3e. On the other hand, for the Pfaffian and anti-Pfaffian states the maximal Fano factor is 2*3.2e. We also systematically study the transport properties of long line junctions between a 5/2 FQH liquid and (i) another 5/2 liquid, (ii) an integer quantum Hall liquid, and (iii) a quantum wire. We study six candidates – two Abelian and four non-Abelian – for the 5/2 FQH effect. This momentum-resolved tunneling provides information about the number, propagation directions, and other features of the edge modes and thus helps distinguish several competing models of the 5/2 state. In the final section of the thesis, we derive a fluctuation-dissipation theorem (FDT) for a general chiral system in a non-equilibrium steady state. We consider a three-terminal system with a chiral edge channel connecting the source and drain terminals. We prove that the cross noise between the currents of the chiral edge and the third terminal is related to the differential conductance of the third terminal. The relation has the same structure as the equilibrium FDT with the nonlinear response in place of the linear conductance. The result can be useful for detecting ''upstream'' modes on quantum Hall edges. We also derive a FDT for heat and charge currents in multi-terminal setups. Advisors/Committee Members: Feldman, Dmitri (Director), Marston, John (Reader), Mitrovic, Vesna (Reader).

Subjects/Keywords: fractional quantum Hall effect

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APA (6^th Edition):

Wang, C. (2012). Transport in Quantum Hall Systems: Probing Anyons and Edge Physics. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:297718/

Chicago Manual of Style (16^th Edition):

Wang, Chenjie. “Transport in Quantum Hall Systems: Probing Anyons and Edge Physics.” 2012. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:297718/.

MLA Handbook (7^th Edition):

Wang, Chenjie. “Transport in Quantum Hall Systems: Probing Anyons and Edge Physics.” 2012. Web. 05 Dec 2020.

Vancouver:

Wang C. Transport in Quantum Hall Systems: Probing Anyons and Edge Physics. [Internet] [Doctoral dissertation]. Brown University; 2012. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:297718/.

Council of Science Editors:

Wang C. Transport in Quantum Hall Systems: Probing Anyons and Edge Physics. [Doctoral Dissertation]. Brown University; 2012. Available from: https://repository.library.brown.edu/studio/item/bdr:297718/

8. Hanson, Helen A. The Crystallography of Vortex Matter in a Niobium Crystal.

Degree: PhD, Physics, 2012, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:297704/

► The vortex matter in type-II superconductors continues to be a subject of great fascination in condensed matter physics. A longstanding theoretical and experimental problem is… (more)

▼ The vortex matter in type-II superconductors continues to be a subject of great fascination in condensed matter physics. A longstanding theoretical and experimental problem is the identification of the ground state of the vortex lines in the presence of quenched atomic disorder which acts as random pinning centers. A possible edge contamination model has been proposed as a mechanism behind the seemingly contradictory experimental results for the ordered state of matter. This model could also explain the lack of universality for the peak effect behavior exhibited in samples with otherwise similar phase diagrams. Using a novel neutron diffraction technique, we report structural evidence for this edge contamination mechanism. This high-resolution method is used to study the fine structure of the vortex matter in a niobium crystal with a weak peak effect and a disordered zero-field-cooled vortex matter. We find this disordered state is metastable and that it can be restructured through a thermal cycling procedure. The results are explained in a strained lattice framework. We then perform Reverse Monte Carlo Refinements on our neutron scattering data and the possible vortex structures for our crystal agree with experimental results from an approach that combines spatial information with reciprocal space scattering. Having confirmed the existence of an edge contamination mechanism in this sample, we oxidize the surface in order to reduce the impact of the inhomogeneous surface barrier. By repeating our neutron diffraction measurements, we find that oxidation process has smoothed the magnetic field profile through the sample and improves the overall structural order of the zero-field-cooled vortex matter. On the other hand, the field-cooled vortex matter structure should be independent of any edge contamination effect but surprisingly, this scattering intensity in fact doubles after surface oxidation. This result suggests that there is another source of disorder in the niobium crystal that has been affected. We discuss our results in the context of the peak effect and Bragg glass models. Advisors/Committee Members: Ling, Xinsheng (Director), Kosterlitz, James (Reader), Mitrovic, Vesna (Reader).

Subjects/Keywords: vortex phyiscs

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APA (6^th Edition):

Hanson, H. A. (2012). The Crystallography of Vortex Matter in a Niobium Crystal. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:297704/

Chicago Manual of Style (16^th Edition):

Hanson, Helen A. “The Crystallography of Vortex Matter in a Niobium Crystal.” 2012. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:297704/.

MLA Handbook (7^th Edition):

Hanson, Helen A. “The Crystallography of Vortex Matter in a Niobium Crystal.” 2012. Web. 05 Dec 2020.

Vancouver:

Hanson HA. The Crystallography of Vortex Matter in a Niobium Crystal. [Internet] [Doctoral dissertation]. Brown University; 2012. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:297704/.

Council of Science Editors:

Hanson HA. The Crystallography of Vortex Matter in a Niobium Crystal. [Doctoral Dissertation]. Brown University; 2012. Available from: https://repository.library.brown.edu/studio/item/bdr:297704/

9. Liu, Wencong. NMR Study of Materials with Significant Spin-Orbit Coupling and Transparent Oxide Films.

Degree: Department of Physics, 2017, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:792641/

► Spin-orbit coupling (SOC) refers to the interaction between the orbital angular momentum and electron spin, which is typically a small perturbation in relative light elements.… (more)

▼ Spin-orbit coupling (SOC) refers to the interaction between the orbital angular momentum and electron spin, which is typically a small perturbation in relative light elements. However, such interaction is proportional to the fourth order of the atomic number and could be quite significant for heavy elements. Exotic physics arising from significant SOC include the emergent phases in Mott insulators with strong SOC and the exploded works on topological insulators (TI). For the first research thread, the combined effects of strong electronic correlations with SOC can lead to a plethora of emergent novel quantum states. The second research thread which also involves strong SOC and correlated electrons lies at the intersection of topological insulator and Kondo insulator. In this thesis, we first present an extensive nuclear magnetic resonance (NMR) study of 23Na in Ba2NaOsO6, a typical Mott insulator with SOC. We measured 23Na NMR spectra as a function of temperature in different magnetic fields. The NMR measurements reveals a paramagnetic at high temperatures, a broken local point symmetry (BLPS) phase at intermediate temperatures and a canted ferromagnetic phase at low temperatures. Most importantly, we determine the field-temperature phase diagram of Ba2NaOsO6 which shows that the intermediate BLPS phase extends to wider range in high fields. Furthermore, by adopting numerical calculation, we confirm that the breaking of local point symmetry is not due to trivial intrinsic structure instability but is due to multipolar interaction. Next, angle dependence of NMR spectra show that the canted ferromagnetic order is suppressed along certain direction at low temperatures. Secondly, we performed NMR measurements of spin-lattice relaxation (T1) on 11B of Kondo insulator SmB6 at ultra-low temperatures in various magnetic fields. We observed constant low-energy density-of-states (DOS) which corresponds to gapless excitation. Advisors/Committee Members: Mitrovic, Vesna (Advisor), Valles, James (Reader), Marston, Brad (Reader).

Subjects/Keywords: Nuclear magnetic resonance

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APA (6^th Edition):

Liu, W. (2017). NMR Study of Materials with Significant Spin-Orbit Coupling and Transparent Oxide Films. (Thesis). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:792641/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Liu, Wencong. “NMR Study of Materials with Significant Spin-Orbit Coupling and Transparent Oxide Films.” 2017. Thesis, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:792641/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Liu, Wencong. “NMR Study of Materials with Significant Spin-Orbit Coupling and Transparent Oxide Films.” 2017. Web. 05 Dec 2020.

Vancouver:

Liu W. NMR Study of Materials with Significant Spin-Orbit Coupling and Transparent Oxide Films. [Internet] [Thesis]. Brown University; 2017. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:792641/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Liu W. NMR Study of Materials with Significant Spin-Orbit Coupling and Transparent Oxide Films. [Thesis]. Brown University; 2017. Available from: https://repository.library.brown.edu/studio/item/bdr:792641/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

10. Koutroulakis, Georgios. Unravelling the mysteries of unconventional superconductivity with NMR: The curious case of CeCoIn5.

Degree: PhD, Physics, 2011, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:11206/

► Heavy-fermion materials provide an exceptional setting for the theoretical and experimental study of many intriguing problems of modern condensed matter physics. Quantum criticality, competition of… (more)

▼ Heavy-fermion materials provide an exceptional setting for the theoretical and experimental study of many intriguing problems of modern condensed matter physics. Quantum criticality, competition of Kondo and RKKY interactions, and unconventional superconductivity are only a few of the many examples. One of the most prominent representatives of this family of materials is CeCoIn5, which, due to its rather unique properties, has attracted intense research interest in recent years.In this thesis, we present an extensive low temperature 115In nuclear magnetic resonance (NMR) study of CeCoIn5, with a magnetic field applied parallel to the â-axis of its tetragonal crystal. Our measurements focus on the superconducting region of the H-T phase diagram, exhibiting Tc ~2.3 K and Hc2 ~11.8 T. Through a consistent and thorough analysis of the NMR observables, our investigation reveals clear evidence of two separate phases within the superconducting state and helps elucidate the details of their nature. In particular, the first phase (referred to as LFSC), which occupies most of the "volume" of the superconducting state, is found to be well-described by a Ginzburg-Landau model for the vortex lattice in an unconventional superconductor of dx2-y2 gap symmetry. The second phase (referred to as HFLT), stabilized at a narrow high field, low temperature corner of the phase diagram in the vicinity of Hc2, shows signs of spatially modulated superconductivity. This is interpreted as a likely realization of the elusive novel superconducting phase theoretically predicted by Fulde, Ferrell, Larkin, and Ovchinnikov in the 1960s. What is more, a long range magnetic order is established within the limits of this phase, associated with an incommensurate spin-density wave order. Lastly, an additional region of distinct behavior is identified, lying in between the LFSC and HFLT phases, which is possibly a true FFLO state in the presence of strong antiferromagnetic fluctuations.These results provide, as a whole, a remarkable insight into unconventional superconductivity and quantum magnetism, as well as their intricate interplay, not only in heavy fermion materials but in condensed matter systems in general. Advisors/Committee Members: Mitrovic, Vesna (Director), Marston, John (Reader), Valles, James (Reader).

Subjects/Keywords: heavy-fermions

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APA (6^th Edition):

Koutroulakis, G. (2011). Unravelling the mysteries of unconventional superconductivity with NMR: The curious case of CeCoIn5. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:11206/

Chicago Manual of Style (16^th Edition):

Koutroulakis, Georgios. “Unravelling the mysteries of unconventional superconductivity with NMR: The curious case of CeCoIn5.” 2011. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:11206/.

MLA Handbook (7^th Edition):

Koutroulakis, Georgios. “Unravelling the mysteries of unconventional superconductivity with NMR: The curious case of CeCoIn5.” 2011. Web. 05 Dec 2020.

Vancouver:

Koutroulakis G. Unravelling the mysteries of unconventional superconductivity with NMR: The curious case of CeCoIn5. [Internet] [Doctoral dissertation]. Brown University; 2011. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:11206/.

Council of Science Editors:

Koutroulakis G. Unravelling the mysteries of unconventional superconductivity with NMR: The curious case of CeCoIn5. [Doctoral Dissertation]. Brown University; 2011. Available from: https://repository.library.brown.edu/studio/item/bdr:11206/

11. Zhang, Wenzhe. Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions.

Degree: PhD, Physics, 2012, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:297711/

► We systematically studied the spin-dependent transport and electrical noise characteristics of MgO-based magnetic tunnel junctions (MTJs). Utilizing the coherent tunneling effect in the MgO tunnel… (more)

▼ We systematically studied the spin-dependent transport and electrical noise characteristics of MgO-based magnetic tunnel junctions (MTJs). Utilizing the coherent tunneling effect in the MgO tunnel barrier, we have successfully fabricated MTJ devices with large tunneling magnetoresistance (TMR) ratios. To explore the magnetization properties of these devices at a fundamental level, we first investigated the magnetization dynamics of sputtered CoFeB thin films used as the free layers in MgO-based MTJ stacks by a broad-band FMR spectrometer. Then we presented a new method for estimating the magnetic anisotropy dispersion in MTJ arrays in serial configurations, using the simulated field sensitivity maps. Based on a revised Stoner-Wohlfarth model, we were able to assign dispersion parameters to an actual MTJ array with arbitrary magnetic attributes such as TMR ratio, coercivity and hysteresis loops. As a result of our work, the field sensitivity of an MTJ array was found to be inversely correlated to its anisotropy dispersion and magnetic coercivity. In the second part, we focused on the noise properties of MTJ systems. At low frequencies, the flicker noise was measured in two distinct MTJ arrays: MTJ Wheatstone bridges and MTJ discrete resistors, each in their own serial arrays. For MTJ bridges, the statistical dispersion in device resistance and normalized voltage noise were attributed to the greater-than-expected magnetization noise, whereas magnetic coupling among tightly-packed MTJ elements was found to amplify the magnetic fluctuations in the MTJ discrete resistors. Finally, high frequency shot noise measurements were carried out to study the spin-dependent charge transport in MTJ systems. The normalized shot noise, or Fano factor, exhibited a sinusoidal-like variation with a continuous change in the relative orientation between the magnetization vectors of MTJ free and reference layers. We explained the noise behavior with a model of sequential tunneling in the spin-blockade regime, in which the faster transport of majority spin electrons in tunnel barriers is modulated by the slower tunneling of minority spin electrons. Advisors/Committee Members: Xiao, Gang (Director), Mitrovic, Vesna (Reader), Dell'Antonio, Ian (Reader).

Subjects/Keywords: magnetic tunnel junctions

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APA (6^th Edition):

Zhang, W. (2012). Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:297711/

Chicago Manual of Style (16^th Edition):

Zhang, Wenzhe. “Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions.” 2012. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:297711/.

MLA Handbook (7^th Edition):

Zhang, Wenzhe. “Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions.” 2012. Web. 05 Dec 2020.

Vancouver:

Zhang W. Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions. [Internet] [Doctoral dissertation]. Brown University; 2012. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:297711/.

Council of Science Editors:

Zhang W. Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions. [Doctoral Dissertation]. Brown University; 2012. Available from: https://repository.library.brown.edu/studio/item/bdr:297711/

12. Wang, Xi. 3D Neutron Diffraction Studies on the Vortex Lattice.

Degree: PhD, Physics, 2012, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:297705/

► In condensed matter physics the vortex lattice of type-II superconductors provides a prototype for studying the effect of random pinning on elastic systems. One important… (more)

▼ In condensed matter physics the vortex lattice of type-II superconductors provides a prototype for studying the effect of random pinning on elastic systems. One important problem is to understand the structural transition from a theoretically predicted ordered Bragg glass phase to a disordered vortex liquid phase. Defects, such as screw dislocations, should play an important role in mediating this order-disorder transition. It is important to confirm the existence of these defect structures in the vortex lattice. Experimentally it is difficult to probe the detailed defect structures inside the vortex lattice. Traditional methods can only provide information on the surface configuration or an averaged picture of the bulk behavior of the vortex lattice. Here we use a novel high-resolution neutron diffraction technique to probe the angular orientation of the lattice planes as the flux lines traverse the atomic crystal. Our results provide structural evidence for screw dislocations inside the vortex lattice. The anisotropic defect structure in the underlying atomic lattice serves as a symmetry breaking field for the vortex lattice. The strong dependence of the vortex lattice structure on the growth procedure reveals that the system is metastable and can be perturbed through thermal cycling to a possible ground state. We measure the structure of the vortex lattice under different applied magnetic fields and temperatures to study the interplay between vortex-vortex interaction, vortex-atomic lattice interaction, and thermal fluctuations. This high-resolution neutron diffraction technique opens up a new way in studying the detailed structure of the vortex lattice. Our results suggest that the vortex lattice in low temperature superconductors with anisotropic defects in the atomic lattice could be an excellent candidate for exploring the entangled flux liquid phase. Advisors/Committee Members: Ling, Xinsheng (Director), Kosterlitz, J. (Reader), Mitrovic, Vesna (Reader).

Subjects/Keywords: neutron diffraction

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Wang, X. (2012). 3D Neutron Diffraction Studies on the Vortex Lattice. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:297705/

Chicago Manual of Style (16^th Edition):

Wang, Xi. “3D Neutron Diffraction Studies on the Vortex Lattice.” 2012. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:297705/.

MLA Handbook (7^th Edition):

Wang, Xi. “3D Neutron Diffraction Studies on the Vortex Lattice.” 2012. Web. 05 Dec 2020.

Vancouver:

Wang X. 3D Neutron Diffraction Studies on the Vortex Lattice. [Internet] [Doctoral dissertation]. Brown University; 2012. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:297705/.

Council of Science Editors:

Wang X. 3D Neutron Diffraction Studies on the Vortex Lattice. [Doctoral Dissertation]. Brown University; 2012. Available from: https://repository.library.brown.edu/studio/item/bdr:297705/

13. Yang, Guang. Topological Order in Superconductors and Quantum Hall Liquids.

Degree: PhD, Physics, 2014, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:386208/

► Fractional quantum Hall (FQH) liquids are interesting two-dimensional electron systems that possess quasiparticle excitations with fractional charges, obeying quantum statistics different from those of bosons… (more)

▼ Fractional quantum Hall (FQH) liquids are interesting two-dimensional electron systems that possess quasiparticle excitations with fractional charges, obeying quantum statistics different from those of bosons and fermions. In particular, the FQH liquid at filling factor 5/2 was proposed to host Majorana bound state (MBS) with exotic non-Abelian statistics. A collection of MBSs can span a topological Hilbert space, in which each many-particle state is topologically distinct, depending on the historical trajectories of all the MBSs in the system. Logic operations in quantum computation can be encoded in the linear transformations in topological Hilbert space and in principle be protected against local defects and perturbations, which are topologically trivial and cannot induce transitions between different many-particle states. Despite such intriguing theoretical picture, experiments probing the nature of the 5/2 FQH liquid are controversial. In this dissertation, we provide an explanation of two seemingly contradicting experiments in the 5/2 FQH liquid, by exploring the role of electrostatic interaction closely related to the geometries of the devices. We also construct several new 5/2 FQH states, by making use of the particle-hole symmetry in FQH systems, to account for a recent experiment observing upstream neutral edge transport in the 5/2 FQH liquid, which ruled out most of the existing theories. In addition to the new particle-hole states, we propose another topological description of the 5/2 FQH liquid which reconciles all existing transport experiments. Later, we turn our attention to the MBSs in superconductor systems. We study the approaches to minimizing the decoherence of a Majorana-fermion-based qbit due to its interaction with environment, based on a full classification of the fermionic zero modes in a system of interacting Majorana fermions. Advisors/Committee Members: Feldman, Dmitri (Director), Kosterlitz, John (Reader), Mitrovic, Vesna (Reader).

Subjects/Keywords: topological order

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APA (6^th Edition):

Yang, G. (2014). Topological Order in Superconductors and Quantum Hall Liquids. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:386208/

Chicago Manual of Style (16^th Edition):

Yang, Guang. “Topological Order in Superconductors and Quantum Hall Liquids.” 2014. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:386208/.

MLA Handbook (7^th Edition):

Yang, Guang. “Topological Order in Superconductors and Quantum Hall Liquids.” 2014. Web. 05 Dec 2020.

Vancouver:

Yang G. Topological Order in Superconductors and Quantum Hall Liquids. [Internet] [Doctoral dissertation]. Brown University; 2014. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:386208/.

Council of Science Editors:

Yang G. Topological Order in Superconductors and Quantum Hall Liquids. [Doctoral Dissertation]. Brown University; 2014. Available from: https://repository.library.brown.edu/studio/item/bdr:386208/

14. 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 (6^th 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 (16^th Edition):

Hollen, Shawna M. “Cooper Pair Localization in Thin Films near the Superconductor-Insulator Transition.” 2013. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:320462/.

MLA Handbook (7^th Edition):

Hollen, Shawna M. “Cooper Pair Localization in Thin Films near the Superconductor-Insulator Transition.” 2013. Web. 05 Dec 2020.

Vancouver:

Hollen SM. Cooper Pair Localization in Thin Films near the Superconductor-Insulator Transition. [Internet] [Doctoral dissertation]. Brown University; 2013. [cited 2020 Dec 05]. 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/

15. Hu, Rongwei. Investigation of a d-electron Kondo insulator FeSb2.

Degree: PhD, Physics, 2009, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:185/

► FeSb2 is a narrow band semiconductor, whose magnetic susceptibility strongly resembles that of FeSi, an archetype example of Kondo insulator. The unusual spectral weight transfer… (more)

▼ FeSb2 is a narrow band semiconductor, whose magnetic susceptibility strongly resembles that of FeSi, an archetype example of Kondo insulator. The unusual spectral weight transfer in the optical conductivity measurement and ab initio LDA+U calculations imply that FeSb2 is an unconventional semiconductor with strong electron correlations. In order to study the anisotropy and probe the electronic structure of FeSb2, single crystals are grown by high temperature flux method and carriers are introduced into FeSb2 by substituting Fe and Sb with Co/Cr and Te respectively. We investigated the magnetic and electrical properties of FeSb2 and the doping effects. Hall measurement on FeSb2 reveals that multiple band carriers with very large mobility difference are involved in the electrical transport. This can be explained by the orbital selective hybridization of the Fe d-orbitals with Sb-p electrons in FeSb2 involving only one electronic subsystem. Band structure calculation suggests that FeSb2 is close to a magnetic instability. Indeed, various magnetic orders are experimentally observed in doped FeSb2. For example, the activated Pauli paramagnetism of FeSb2 evolves into a weak ferromagnetism in Fe1-xCoxSb2 and a complex canted antiferromagnetic structure in Fe1-xCrxSb2 and Fe(Sb1-xTex)2. Metallic states are readily induced by doping FeSb2 as a result of band filling. Positive colossal magnetoresistance mainly attributed to quasi 1D weak localization is observed in Co doped FeSb2. With Te substitution, FeSb2 evolves from a strongly correlated semiconductor into a moderate heavy fermion metal. Most of the Kondo insulator materials are cubic, with the exception of CeRhSb and CeNiSn, and 4f intermetallics. An important question is that if the Kondo insulator scenario can be applied to 3d materials, e.g. FeSi and FeSb2. FeSb2 can be obtained in single crystal form with high quality and can be readily doped with carriers, thus it represents a model system with only 3d elements to study this physics. Our results indicate that the underling physics of FeSb2 can be well described by the Kondo insulator picture and FeSb2 resembles FeSi in many ways as a prototypical example of a nonrare-earth containing Kondo insulator. Advisors/Committee Members: Mitrovic, Vesna (director), Petrovic, Cedomir (director), Marston, Brad (reader), Valles, James (reader).

Subjects/Keywords: Kondo Insulator

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APA (6^th Edition):

Hu, R. (2009). Investigation of a d-electron Kondo insulator FeSb2. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:185/

Chicago Manual of Style (16^th Edition):

Hu, Rongwei. “Investigation of a d-electron Kondo insulator FeSb2.” 2009. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:185/.

MLA Handbook (7^th Edition):

Hu, Rongwei. “Investigation of a d-electron Kondo insulator FeSb2.” 2009. Web. 05 Dec 2020.

Vancouver:

Hu R. Investigation of a d-electron Kondo insulator FeSb2. [Internet] [Doctoral dissertation]. Brown University; 2009. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:185/.

Council of Science Editors:

Hu R. Investigation of a d-electron Kondo insulator FeSb2. [Doctoral Dissertation]. Brown University; 2009. Available from: https://repository.library.brown.edu/studio/item/bdr:185/

16. Song, Yang. Characteristics and Stability of High Performance Indium Zinc Oxide Thin Film Transistors.

Degree: Department of Physics, 2018, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:792638/

► Amorphous oxide semiconductors (AOSs) have been intensively studied during the last 15 years due to their superior properties. The major application of AOS thin film… (more)

▼ Amorphous oxide semiconductors (AOSs) have been intensively studied during the last 15 years due to their superior properties. The major application of AOS thin film transistors (TFTs) is displays. Compared to the previous generation TFT material—amorphous silicon (a-Si)—AOSs have higher mobility, and can be easily deposited by various deposition techniques at room temperature on arbitrary substrates. This thesis focuses on the characteristics and stability of a specific AOS, amorphous indium zinc oxide (a-IZO), as an electronic material for TFTs. We have fabricated a-IZO TFTs with a top-gate structure by using the in-situ gate dielectric formation technique: some metals—such as Al and Hf—can react with IZO to form an oxide insulator layer in the absence of kinetic constraints. The in-situ dielectric formation can provide a high-quality insulator/IZO interface with a low interface trap density, leading to excellent TFT performance. The subthreshold slope in our best IZO TFTs reaches a value of 62 mV/decade, close to the room temperature theoretical limit, and our devices also show on/off current ratios above 10⁷ and a high extracted field effect mobility around 100 cm2/V·s. These are state-of-the-art results in AOS TFTs. Another focus in our work is the stability of IZO TFTs, where oxygen vacancy generation and migration are used to explain the observed experimental threshold voltage shifts in a-IZO TFTs as a function of aging and applied gate bias. As a possible future research direction, the high electron mobility and controllable high electron density make a-IZO a promising candidate for high-speed, high-power radio frequency transistors. We propose a vertical transistor structure with buried multi-gate fingers. Unlike in the previously studied single-crystal nanowire or permeable base vertical transistors, the properties of a-IZO make it possible to regrow the vertical semiconductor channels without any high temperature epitaxy, lowering fabrication complexity and cost while making the vertical IZO device compatible with arbitrary substrates. Preliminary fabrication process and characterization results of the vertical-current-flow a-IZO TFT are shown and discussed. Advisors/Committee Members: Zaslavsky, Alexander (Advisor), Paine, David (Advisor), Valles, James (Reader), Mitrovic, Vesna (Reader).

Subjects/Keywords: Indium zinc oxide

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APA (6^th Edition):

Song, Y. (2018). Characteristics and Stability of High Performance Indium Zinc Oxide Thin Film Transistors. (Thesis). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:792638/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Song, Yang. “Characteristics and Stability of High Performance Indium Zinc Oxide Thin Film Transistors.” 2018. Thesis, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:792638/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Song, Yang. “Characteristics and Stability of High Performance Indium Zinc Oxide Thin Film Transistors.” 2018. Web. 05 Dec 2020.

Vancouver:

Song Y. Characteristics and Stability of High Performance Indium Zinc Oxide Thin Film Transistors. [Internet] [Thesis]. Brown University; 2018. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:792638/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Song Y. Characteristics and Stability of High Performance Indium Zinc Oxide Thin Film Transistors. [Thesis]. Brown University; 2018. Available from: https://repository.library.brown.edu/studio/item/bdr:792638/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

17. Luo, Xu. Thermodynamic Studies of Phase Transitions and Emerging Orders in Unconventional Superconductors.

Degree: PhD, Physics, 2015, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:419516/

► The nematic phase transition in Fe-based superconductors (FeSCs) has been a topic under intensive investigation. So far it is commonly accepted that the structural transition… (more)

▼ The nematic phase transition in Fe-based superconductors (FeSCs) has been a topic under intensive investigation. So far it is commonly accepted that the structural transition from tetragonal (C4) to orthorhombic (C2) symmetry in FeSCs has an electronic nematic origin due to the unusual anisotropy in resistivity, optical conductivity and orbital occupancy observed above the structural transition. However, recent studies of (Ba, Eu)Fe2(As1-xPx)2 by magnetic torque measurements show the existence of a “true” nematic transition well above the commonly accepted structural/nematic transition .Controversies about this “true” nematic phase transition arise as residue strains or external applied fields are known to break C4 symmetry and render the structural transition merely a crossover. We performed high resolution AC micro-calorimetry and SQUID magnetometry measurements of BaFe2(As1-xPx)2 (x=0, 0.3) to investigate the various phase transitions and to explore the “true” nematic phase transition. The advantageous design of our membrane calorimeter allows us to perform high resolution studies of the thermodynamic phase transitions without any symmetry breaking fields. Our results suggest that there is not a second order “true” nematic phase transition in BaFe2(As1-xPx)2 even though the Ginzburg-Landau model used to fit the magnetic torque data indicates that the expected thermal anomaly should be within our experimental resolution. In addition to the above, we present specific heat and magnetization studies of Ba1-xNaxFe2As2 in search of the recent discovered emergent reentrant C2 to C4 symmetry SDW transition in this series of compound. Our results indeed locate a new phase transition in Ba0.74Na0.26Fe2As2 at 45K. However, the absence of the conventional SDW transition at around 80K in our data leaves doubt about the exact nature of this new phase transition. We also systematically studied the effects of heavy ion irradiation (HII) on the anisotropy of YBCO single crystals by angular rotation specific heat measurements. We found that the anisotropy of YBCO decreases by approximately a factor of two with an irradiation dose of 6T (matching field). The dependence of anisotropy on irradiation doses agrees well with the prediction from a simple phenomenological model that takes into account the anisotropic scattering caused by columnar defects created in HII. Advisors/Committee Members: Ling, Xinsheng (Director), Welp, Ulrich (Director), Marston, John (Reader), Mitrovic, Vesna (Reader).

Subjects/Keywords: Fe-based superconductor

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APA (6^th Edition):

Luo, X. (2015). Thermodynamic Studies of Phase Transitions and Emerging Orders in Unconventional Superconductors. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:419516/

Chicago Manual of Style (16^th Edition):

Luo, Xu. “Thermodynamic Studies of Phase Transitions and Emerging Orders in Unconventional Superconductors.” 2015. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:419516/.

MLA Handbook (7^th Edition):

Luo, Xu. “Thermodynamic Studies of Phase Transitions and Emerging Orders in Unconventional Superconductors.” 2015. Web. 05 Dec 2020.

Vancouver:

Luo X. Thermodynamic Studies of Phase Transitions and Emerging Orders in Unconventional Superconductors. [Internet] [Doctoral dissertation]. Brown University; 2015. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:419516/.

Council of Science Editors:

Luo X. Thermodynamic Studies of Phase Transitions and Emerging Orders in Unconventional Superconductors. [Doctoral Dissertation]. Brown University; 2015. Available from: https://repository.library.brown.edu/studio/item/bdr:419516/

18. Law, Kam Tuen. Probing Abelian and Non-Abelian Statistics in Fractional Quantum Hall States.

Degree: PhD, Physics, 2008, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:17/

► Particles other than bosons and fermions can exist in two dimensions. One possibility is that when one particle makes a circle around another particle the… (more)

Subjects/Keywords: Anyonic Statistics

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APA (6^th Edition):

Law, K. T. (2008). Probing Abelian and Non-Abelian Statistics in Fractional Quantum Hall States. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:17/

Chicago Manual of Style (16^th Edition):

Law, Kam Tuen. “Probing Abelian and Non-Abelian Statistics in Fractional Quantum Hall States.” 2008. Doctoral Dissertation, Brown University. Accessed December 05, 2020. https://repository.library.brown.edu/studio/item/bdr:17/.

MLA Handbook (7^th Edition):

Law, Kam Tuen. “Probing Abelian and Non-Abelian Statistics in Fractional Quantum Hall States.” 2008. Web. 05 Dec 2020.

Vancouver:

Law KT. Probing Abelian and Non-Abelian Statistics in Fractional Quantum Hall States. [Internet] [Doctoral dissertation]. Brown University; 2008. [cited 2020 Dec 05]. Available from: https://repository.library.brown.edu/studio/item/bdr:17/.

Council of Science Editors:

Law KT. Probing Abelian and Non-Abelian Statistics in Fractional Quantum Hall States. [Doctoral Dissertation]. Brown University; 2008. Available from: https://repository.library.brown.edu/studio/item/bdr:17/

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