Counterpropagating topological and quantum Hall edge channels

TL;DR

This study reveals that in disordered 2D topological insulators under high magnetic fields, topological and quantum Hall edge channels coexist, challenging previous expectations of a transport gap and highlighting the role of disorder in edge state behavior.

Contribution

It demonstrates the coexistence of topological and quantum Hall edge channels in disordered systems under strong magnetic fields, revealing new insights into edge state resilience and disorder effects.

Findings

Absence of expected transport gap in disordered samples at high magnetic fields

Coexistence of topological and quantum Hall edge channels observed

Disorder influences the formation of extended quantum Hall edge channels along charge puddles

Abstract

The survival of the quantum spin Hall edge channels in presence of an external magnetic field has been a subject of experimental and theoretical research. The inversion of Landau levels that accommodates the quantum spin Hall effect is destroyed at a critical magnetic field, and a trivial insulating gap appears in the spectrum for stronger fields. In this work, we report the absence of this transport gap in disordered two dimensional topological insulators in perpendicular magnetic fields of up to 16 T. Instead, we observe that a topological edge channel (from band inversion) coexists with a counterpropagating quantum Hall edge channel for magnetic fields at which the transition to the insulating regime is expected. For larger fields, we observe only the quantum Hall edge channel with transverse resistance close to $h/e^2$. By tuning the disorder using different fabrication processes, we find evidence that this unexpected $\nu=1$ plateau originates from extended quantum Hall edge channels along a continuous network of charge puddles at the edges of the device.