Nonlocal resistance and its fluctuations in microstructures of band-inverted HgTe/(Hg,Cd)Te quantum wells

TL;DR

This study experimentally investigates edge channel transport in HgTe/HgCdTe quantum wells, revealing short topological protection lengths and the influence of charge puddles on resistance fluctuations in a two-dimensional topological insulator.

Contribution

It provides new insights into the limitations of topological protection in HgTe quantum wells and the role of charge puddles in resistance behavior.

Findings

Edge channels carry current in the depletion regime.

Topological protection length is much shorter than the channel length (~100 μm).

Resistance fluctuations are influenced by charge puddles.

Abstract

We investigate experimentally transport in gated microsctructures containing a band-inverted HgTe/Hg_{0.3}Cd_{0.7}Te quantum well. Measurements of nonlocal resistances using many contacts prove that in the depletion regime the current is carried by the edge channels, as expected for a two-dimensional topological insulator. However, high and non-quantized values of channel resistances show that the topological protection length (i.e. the distance on which the carriers in helical edge channels propagate without backscattering) is much shorter than the channel length, which is ~100 micrometers. The weak temperature dependence of the resistance and the presence of temperature dependent reproducible quasi-periodic resistance fluctuations can be qualitatively explained by the presence of charge puddles in the well, to which the electrons from the edge channels are tunnel-coupled.