Non-linear ballistic response of quantum spin-Hall edge states

TL;DR

This paper investigates the non-linear electrical response of quantum spin-Hall edge states, revealing how it uncovers symmetry-breaking effects and deviations from linear dispersion, crucial for understanding topological transport.

Contribution

It provides the first detailed analysis of the non-linear ballistic response of topological edge states, linking response features to edge dispersion and symmetry breaking.

Findings

Non-linear response indicates symmetry breaking in edge dispersion

Discontinuities in band occupation cause non-linear effects

Edge dispersion characterized for various topological materials

Abstract

Topological edge states exhibit dissipationless transport and electrically-driven topological phase transitions, making them ideal for next-generation transistors that are not constrained by Moore's law. Nevertheless, their dispersion has never been probed and is often assumed to be simply linear, without any rigorous justification. Here we determine the non-linear electrical response of topological edge states in the ballistic regime and demonstrate the way this response ascertains the presence of symmetry breaking terms in the edge dispersion, such as deviations from non-linearity and tilted spin quantization axes. The non-linear response stems from discontinuities in the band occupation on either side of a Zeeman gap, and its direction is set by the spin orientation with respect to the Zeeman field. We determine the edge dispersion for several classes of topological materials and discuss experimental measurement.