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Electronic states in disordered topological insulators

Citation

Kim, Kun Woo (2014) Electronic states in disordered topological insulators. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:06022014-093929164

Abstract

We present a theoretical study of electronic states in topological insulators with impurities. Chiral edge states in 2d topological insulators and helical surface states in 3d topological insulators show a robust transport against nonmagnetic impurities. Such a nontrivial character inspired physicists to come up with applications such as spintronic devices [1], thermoelectric materials [2], photovoltaics [3], and quantum computation [4]. Not only has it provided new opportunities from a practical point of view, but its theoretical study has deepened the understanding of the topological nature of condensed matter systems. However, experimental realizations of topological insulators have been challenging. For example, a 2d topological insulator fabricated in a HeTe quantum well structure by Konig et al. [5] shows a longitudinal conductance which is not well quantized and varies with temperature. 3d topological insulators such as Bi2Se3 and Bi2Te3 exhibit not only a signature of surface states, but they also show a bulk conduction [6]. The series of experiments motivated us to study the effects of impurities and coexisting bulk Fermi surface in topological insulators. We first address a single impurity problem in a topological insulator using a semiclassical approach. Then we study the conductance behavior of a disordered topological-metal strip where bulk modes are associated with the transport of edge modes via impurity scattering. We verify that the conduction through a chiral edge channel retains its topological signature, and we discovered that the transmission can be succinctly expressed in a closed form as a ratio of determinants of the bulk Green's function and impurity potentials. We further study the transport of 1d systems which can be decomposed in terms of chiral modes. Lastly, the surface impurity effect on the local density of surface states over layers into the bulk is studied between weak and strong disorder strength limits.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:topological insulator, impurity, electronic transport, electronic local density of states, surface states in topological insulators, semiclassical approach, disordered topological metal-strip
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Applied Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Refael, Gil
Group:Institute for Quantum Information and Matter, IQIM
Thesis Committee:
  • Cross, Michael Clifford (chair)
  • Motrunich, Olexei I.
  • Hsieh, David
  • Refael, Gil
Defense Date:27 May 2014
Record Number:CaltechTHESIS:06022014-093929164
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:06022014-093929164
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8462
Collection:CaltechTHESIS
Deposited By: Kun Woo Kim
Deposited On:03 Jun 2014 19:10
Last Modified:14 Jun 2017 16:47

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