Spatially resolved study of backscattering in the quantum spin Hall state

TL;DR

This study uses scanning gate microscopy to locally investigate backscattering in quantum spin Hall edge states, revealing localized scattering sites that affect transport and demonstrating robustness in unperturbed regions.

Contribution

It introduces a local probing method to identify scattering sites in QSH edge states, advancing understanding of their microscopic transport properties.

Findings

Localized scattering sites limit non-dissipative transport

Edge states are robust against weak potential fluctuations

Unperturbed propagation observed between scattering sites

Abstract

The discovery of the Quantum Spin Hall state, and topological insulators in general, has sparked strong experimental efforts. Transport studies of the Quantum Spin Hall state confirmed the presence of edge states, showed ballistic edge transport in micron-sized samples and demonstrated the spin polarization of the helical edge states. While these experiments have confirmed the broad theoretical model, the properties of the QSH edge states have not yet been investigated on a local scale. Using Scanning Gate Microscopy to perturb the QSH edge states on a sub-micron scale, we identify well-localized scattering sites which likely limit the expected non-dissipative transport in the helical edge channels. In the micron-sized regions between the scattering sites, the edge states appear to propagate unperturbed as expected for an ideal QSH system and are found to be robust against weak induced potential fluctuations.