Interplay of bulk and edge states in transport of two-dimensional topological insulators

TL;DR

This paper investigates how bulk and edge states influence electrical conductance in two-dimensional topological insulators, revealing non-additive effects and non-monotonic conductance behavior in short junctions, with implications for experimental observations.

Contribution

It demonstrates the non-additive interplay of bulk and edge contributions and uncovers non-monotonic conductance behavior in short junctions of 2D topological insulators.

Findings

Conductance from bulk and edge states is not simply additive.

Short junctions exhibit non-monotonic conductance as a function of length.

Robust propagating solutions form, resistant to scalar disorder.

Abstract

We study transport in two-terminal metal/quantum spin-Hall insulator (QSHI)/metal junctions. We show that the conductance signals originating from the bulk and the edge contributions are not additive. While for a long junction the transport is determined by the edge states contribution, for a short junction, the conductance signal is built from both bulk and edge states in the ratio which depends on the width of the sample. Further, in the topological insulator regime the conductance for short junctions shows a non-monotonic behavior as a function of the sample length. Surprisingly this non-monotonic behavior of conductance can be traced to the formation of an effectively propagating solution which is robust against scalar disorder. Our predictions should be experimentally verifiable in HgTe QWs and Bi$_2$Se$_3$ thin films.