Fingerprint of surface and bulk states in transport of 3D topological insulators

点击翻译按钮获取中文摘要

3D topological insulators (TIs) consist of the metallic Dirac–like surface states while the bulk of the material is insulating. Although the Dirac dispersion was observed in angle resolved photoemission experiments, the transport properties of these materials are still in question. This is mainly due to the fact that for the typical 3D TI as Bi2Se3 and Bi2Te3, the bulk conductivity is not negligible and coexistence or coupling between surface and bulk states has to be taken into account. Additionally, each of the surfaces is interconnected in 3D TIs, and the surface has rather the topology of the sphere than an infinite 2D system. Since transport experiments give direct access to the topological invariant in these systems, which in the case of a single strictly 2D massless Dirac fermion should be the half integer quantum Hall plateaus, the fundamental question asked in this proposal is how both of these mechanisms alter the transport properties and the topological invariant in these materials.We will use both analytical and numerical approaches to understand step by step how the coexistence and coupling of the surface and bulk states modify the transport, galvano-magnetic, and magneto-optical effects in these materials. In particular we intend to study simple junctions between surface states in magnetic fields, different models of surface-bulk coupling and finally full three-dimensional Dirac model discretized on the lattice within non-equilibrium Green function method. The experimentally relevant goal of this proposal is to reconcile the controversy if and when Hall conductivity can be quantized and how the galvano-magnetic and magneto-optical effects are affected by bulk and disorder effects. The fundamental theoretical questions of this proposal are to understand the quantum Hall effect in three-dimensions and to find the conditions for the universality of the topological invariant of 3D TIs in the realistic systems. Is the non-interacting picture sufficient to describe transport properties of 3D TIs?