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# Quantum phases and phase transitions in disordered low-dimensional systems: thin film superconductors, bilayer two-dimensional electron systems, and one-dimensional optical lattices

## Citation

Zou, Yue (2011) Quantum phases and phase transitions in disordered low-dimensional systems: thin film superconductors, bilayer two-dimensional electron systems, and one-dimensional optical lattices. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:09082010-155113346

## Abstract

The study of various quantum phases and the phase transitions between them in low-dimensional disordered systems has been a central theme of recent developments of condensed matter physics. Examples include disordered thin film superconductors, whose critical temperature and density of states can be affected by a normal metallic layer deposited on top of them; amorphous thin films exhibiting superconductor-insulator transitions (SIT) tuned by disorder or magnetic field; and bilayer two-dimensional electron systems at total filling factor $\nu=1$, which exhibit interlayer coherent quantum Hall state at small layer separation and have a phase transition tuned by layer separation, parallel magnetic field, density imbalance, or temperature. Although a lot of theoretical and experimental investigations have been done, many properties of these phases and natures of the phase transitions in these systems are still being debated. Here in this thesis, we report our progress towards a better understanding of these systems. For disordered thin film superconductors, we first propose that the experimentally observed lower-than-theory gap-$T_c$ ratio in bilayer superconducting-normal-metal films is due to inhomogeneous couplings. Next, for films demonstrating superconductor-insulator transitions, we propose a new type of experiment, namely the drag resistance measurement, as a method capable of pointing to the correct theory among major candidates such as the quantum vortex picture and the percolation picture. For bilayer two-dimensional electron systems, we propose that a first-order phase transition scenario and the resulting Clausius-Clapeyron equations can describe various transitions observed in experiments quite well. Finally, in one-dimensional optical lattices, we show that one can engineer the long-sought-after random hopping model with only off-diagonal disorder by fast-modulating an Anderson insulator.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:condensed matter physics; superconductivity; thin-film superconductors; superconductor-insulator transitions; double-layer quantum Hall effect; optical lattices; random hopping models
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
• Refael, Gil
Thesis Committee:
• Refael, Gil (chair)
• Eisenstein, James P.
• Kitaev, Alexei
• Motrunich, Olexei I.
Defense Date:19 May 2010
Record Number:CaltechTHESIS:09082010-155113346
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:09082010-155113346
Related URLs:
URLURL TypeDescription
http://arxiv.org/abs/1007.2245arXivUNSPECIFIED
http://arxiv.org/abs/1005.2597arXivUNSPECIFIED
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6024
Collection:CaltechTHESIS
Deposited By: Yue Zou
Deposited On:01 Nov 2010 21:00