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You searched for +publisher:"University of Southern California" +contributor:("Haselwandter, Christoph"). Showing records 1 – 3 of 3 total matches.

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University of Southern California

1. Trinh, Kien Trong. Phase diagram of disordered quantum antiferromagnets.

Degree: PhD, Physics, 2014, University of Southern California

The presence of disorder can deeply affect the critical behavior of quantum spin systems. Disorder can localize the long-wavelength modes developed at the quantum phase transition of the clean systems, and thus introduce glassy phases. Furthermore, it has been shown that many novel phases can be induced by the simultaneous presence of both magnetic field and geometric randomness. For instance, in doped spin-gap ladders one observes a very rich phase diagram, with a sequence of magnetic field controlled phases, including superfluidity, Bose-Einstein condensate, Bose glass and full polarization. Geometric randomness can also induce local magnetic moments giving rise to long-range order through an order-by-disorder mechanism in a gapped quantum-disordered ground state. In this dissertation, we investigate the physical properties and phase diagrams of doped even-leg ladders. Even-leg ladders are the minimal system in which we can study these effects: pruned spins, bond vs. rung vacancies, and order-by-disorder. Furthermore, such minimal even-leg ladders do not have any intrinsic low-energy degrees of freedom, because the pure system is gapped. Thus the effects of impurity vacancies, introducing new low-energy features, can be cleanly studied. ❧ In the first part, we uncover the effects of quenched disorder in the form of site and bond dilution on the physics of the S=1/2 antiferromagnetic Heisenberg model in even-leg ladders. Site dilution is found to prune rung singlets and thus create localized moments which interact via a random, unfrustrated network of effective couplings, realizing a random-exchange Heisenberg model in one spatial dimension. This system exhibits a power-law diverging correlation length as the temperature decreases. Contrary to previous claims, we observe that the scaling exponent is non-universal, i.e., doping dependent. This finding can be explained by the discrete nature of the values taken by the effective exchange couplings in the doped ladder. Bond dilution of even-leg ladders leads to a more complex evolution with doping. Correlations are weakly enhanced in 2-leg ladders, and are even suppressed for low dilution in the case of 4-leg and 6-leg ladders. We clarify the different aspects of correlation enhancement and suppression due to bond dilution by isolating the contributions of rung-bond dilution and leg-bond dilution. ❧ In the second part, we investigate random bond disorder in antiferromagnetic spin-1/2 Heisenberg ladders. We find that the effects of individual bond impurities vary strongly, depending on their positions on legs and rungs. We initially focus on how the distribution of local bond energies depends on the impurity concentration. Then we study how the phase diagram of even-leg ladders is affected by random bond doping. We observe Bose glass phases in two regimes (h' < h ≲ h{c₁} and h'' < h Advisors/Committee Members: Haas, Stephan W. (Committee Chair), Bickers, Nelson Eugene (Committee Member), Nakano, Aiichiro (Committee Member), Takahashi, Susumu (Committee Member), Haselwandter, Christoph (Committee Member).

Subjects/Keywords: quantum spin liquids; valence bond phases and related phenomena; spin chain models; spin-glass and other random models; effects of disorder; collective effects; collective excitations; exchange interactions; correlation length; quantum Monte Carlo; stochastic series expansion; Heisenberg model; Heisenberg ladders; spin ladders; Bose-Einstein condensate; site dilution; bond dilution; quantum phase transition; Griffiths phase

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

APA (6th Edition):

Trinh, K. T. (2014). Phase diagram of disordered quantum antiferromagnets. (Doctoral Dissertation). University of Southern California. Retrieved from http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/508093/rec/5025

Chicago Manual of Style (16th Edition):

Trinh, Kien Trong. “Phase diagram of disordered quantum antiferromagnets.” 2014. Doctoral Dissertation, University of Southern California. Accessed April 19, 2019. http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/508093/rec/5025.

MLA Handbook (7th Edition):

Trinh, Kien Trong. “Phase diagram of disordered quantum antiferromagnets.” 2014. Web. 19 Apr 2019.

Vancouver:

Trinh KT. Phase diagram of disordered quantum antiferromagnets. [Internet] [Doctoral dissertation]. University of Southern California; 2014. [cited 2019 Apr 19]. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/508093/rec/5025.

Council of Science Editors:

Trinh KT. Phase diagram of disordered quantum antiferromagnets. [Doctoral Dissertation]. University of Southern California; 2014. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/508093/rec/5025


University of Southern California

2. Pirbadian, Sahand. Bacterial nanowires of Shewanella oneidensis MR-1: electron transport mechanism, composition, and role of multiheme cytochromes.

Degree: PhD, Physics, 2015, University of Southern California

In this thesis, we discuss three topics concerning extracellular electron transfer in the Dissimilatory Metal Reducing Bacterium (DMRB) Shewanella oneidensis MR-1. One proposed strategy to accomplish extracellular charge transfer in Shewanella involves forming a conductive pathway to electrodes by incorporating redox components on outer cell membranes and along extracellular appendages known as bacterial nanowires within biofilms. In the first part of this dissertation, to describe extracellular charge transfer in microbial redox chains, we employed a model based on incoherent hopping between sites in the chain and an interfacial treatment of electrochemical interactions with the surrounding electrodes. Based on this model, we calculated the current-voltage (I-V) characteristics and found the results to be in good agreement with I-V measurements across and along individual microbial nanowires produced by the bacterium S. oneidensis MR-1. Based on our analysis, we propose that multistep hopping in redox chains constitutes a viable strategy for extracellular charge transfer in microbial biofilms. ❧ In the second part, we report the first in vivo observations of the formation and respiratory impact of nanowires in the model metal-reducing microbe S. oneidensis MR-1. Live fluorescence measurements, immunolabeling, and quantitative gene expression analysis point to S. oneidensis MR-1 nanowires as extensions of the outer membrane and periplasm that include the multiheme cytochromes responsible for EET, rather than pilin-based structures as previously thought. These membrane extensions are associated with outer membrane vesicles, structures ubiquitous in Gram-negative bacteria, and are consistent with bacterial nanowires that mediate long-range EET by our proposed multistep redox hopping mechanism. Redox-functionalized membrane and vesicular extensions may represent a general microbial strategy for electron transport and energy distribution. ❧ In addition, to elucidate the membranous nature of Shewanella nanowires, we imaged these filaments using Transmission Electron Microscopy. The TEM images reported in this thesis also provide the most accurate estimates of bacterial nanowire dimensions to date. Future TEM and cryo-TEM imaging can establish the specific alignment and configuration of outer membrane cytochromes that facilitate electron transport along bacterial nanowires. ❧ In the third part of this thesis, we focus on the molecular conductance of MtrF, the first decaheme outer membrane cytochrome with a solved crystal structure. Decaheme outer membrane cytochromes of Shewanella play a crucial role in all the suggested pathways of extracellular electron transfer. An understanding of the electron transfer properties in MtrF will therefore impact all aspects of extracellular electron transfer research. In this thesis, using purified MtrF, we form monolayers of the protein on atomically flat gold substrates and address the dry monolayer with a Scanning Tunneling Microscope (STM) tip. This technique can be used in the future… Advisors/Committee Members: El-Naggar, Mohamed Y. (Committee Chair), Haselwandter, Christoph (Committee Member), Kresin, Vitaly V. (Committee Member), Haas, Stephan W. (Committee Member), Finkel, Steven E. (Committee Member).

Subjects/Keywords: Shewanella; bacterial nanowires; extracellular electron transfer; membrane cytochromes; bioelectronics; microbial fuel cells; respiration; membrane extensions; vesicle chain; dissimilatory metal reducing bacteria

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

APA (6th Edition):

Pirbadian, S. (2015). Bacterial nanowires of Shewanella oneidensis MR-1: electron transport mechanism, composition, and role of multiheme cytochromes. (Doctoral Dissertation). University of Southern California. Retrieved from http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/543883/rec/1021

Chicago Manual of Style (16th Edition):

Pirbadian, Sahand. “Bacterial nanowires of Shewanella oneidensis MR-1: electron transport mechanism, composition, and role of multiheme cytochromes.” 2015. Doctoral Dissertation, University of Southern California. Accessed April 19, 2019. http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/543883/rec/1021.

MLA Handbook (7th Edition):

Pirbadian, Sahand. “Bacterial nanowires of Shewanella oneidensis MR-1: electron transport mechanism, composition, and role of multiheme cytochromes.” 2015. Web. 19 Apr 2019.

Vancouver:

Pirbadian S. Bacterial nanowires of Shewanella oneidensis MR-1: electron transport mechanism, composition, and role of multiheme cytochromes. [Internet] [Doctoral dissertation]. University of Southern California; 2015. [cited 2019 Apr 19]. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/543883/rec/1021.

Council of Science Editors:

Pirbadian S. Bacterial nanowires of Shewanella oneidensis MR-1: electron transport mechanism, composition, and role of multiheme cytochromes. [Doctoral Dissertation]. University of Southern California; 2015. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/543883/rec/1021


University of Southern California

3. Song, Kok Wee. Electronic correlation effects in multi-band systems.

Degree: PhD, Physics, 2014, University of Southern California

The recent dominant trends in condensed matter physics research can be roughly summarized into three newly discovered materials: topological insulators, graphene, and iron‐based superconductors. All these materials exhibit many intriguing properties which are fundamentally related to their electronic band structure. Therefore, this lead to many intense investigations on multi‐band electronic system to explore new physics. ❧ The physics of multi‐band electronic structure is fascinating in several aspects. Without many‐body effects, because of the gauge freedom of Bloch states, topological insulators can give rise a robust metallic behavior at its boundaries. In graphene, the touching between conduction and valence band at Fermi level yields a new criticality class which exhibit many unconventional electronic properties, especially its quasi‐relativistic behavior. Turning to the many‐body effects, for instance, the iron‐based superconductors can sustain an superconducting ground state despite of no attractive interactions in the system. Therefore, a deeper understanding for the conventional notions in condensed matter physics has put forward by many of these experimental observations. ❧ In this thesis, the many‐body effects in multi‐band systems are the main focus, especially the study of graphene and iron‐based superconductors which can be compared to experiments. These theoretical studies intend to understand how the underlying electronic bands degree of freedom can give rise to Fermi‐liquid instabilities, and how these effects can be related to intriguing physical properties. ❧ We first study the electrons correlation effects in bilayer graphene by a renormalization group technique. In this study, we build a microscopic model of bilayer graphene from a tight‐binding approach. In our finding, the peculiar Fermi surface configuration leads to critical behavior which is beyond the Fermi‐liquid paradigm. Furthermore, due to the electron‐electron interactions between different bands, excitonic instabilities are found in many different scattering channels. This analysis suggest a collection of competing orders in the system ground states. This result is consistent with the experimental observation that bilayer graphene is an insulator. ❧ Next, we study nematic order in the metallic phase of iron pnictides. In contrast to graphene, the density of states is finite at the Fermi surface. By careful investigating the scattering processes near these Fermi surface, and then identifying the most relevant collective modes from these processes, we find that a Pomeranchuk instability can be driven by magnetic fluctuations. This instability eventually leads to the break down of the isotropic metallic phase which electronic system exhibit broken crystalline rotational symmetry but preserve translation symmetry. As the experiment suggests, this can be a candidate for nematic order in the metallic phase. Advisors/Committee Members: Haas, Stephan W. (Committee Chair), Bickers, Gene (Committee Member), Dappen, Werner (Committee Member), Däppen, Werner (Committee Member), Daeppen, Werner (Committee Member), Haselwandter, Christoph (Committee Member), Jonckheere, Edmond A. (Committee Member).

Subjects/Keywords: excitonic instabilties; Fermi liquid; graphene; iron pnictides; nematic order; superconductivity

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

APA (6th Edition):

Song, K. W. (2014). Electronic correlation effects in multi-band systems. (Doctoral Dissertation). University of Southern California. Retrieved from http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/376102/rec/2275

Chicago Manual of Style (16th Edition):

Song, Kok Wee. “Electronic correlation effects in multi-band systems.” 2014. Doctoral Dissertation, University of Southern California. Accessed April 19, 2019. http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/376102/rec/2275.

MLA Handbook (7th Edition):

Song, Kok Wee. “Electronic correlation effects in multi-band systems.” 2014. Web. 19 Apr 2019.

Vancouver:

Song KW. Electronic correlation effects in multi-band systems. [Internet] [Doctoral dissertation]. University of Southern California; 2014. [cited 2019 Apr 19]. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/376102/rec/2275.

Council of Science Editors:

Song KW. Electronic correlation effects in multi-band systems. [Doctoral Dissertation]. University of Southern California; 2014. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/376102/rec/2275

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