Transport through quantum spin Hall insulator/metal junctions in graphene ribbons

TL;DR

This paper investigates electron transport in graphene ribbons with quantum spin Hall insulator/metal interfaces, demonstrating perfect transmission in clean systems and resilience to disorder with increasing ribbon width.

Contribution

It provides analytical and numerical analysis of topological edge state transmission in graphene ribbons with spin-orbit coupling, highlighting effects of disorder and ribbon width.

Findings

Perfect transmission in clean ribbons regardless of geometry.

Backscattering occurs in disordered ribbons but diminishes with increased width.

Transmission approaches unity as ribbon width increases, even with edge roughness.

Abstract

Quantum spin Hall insulator/metal interfaces are formed in graphene ribbons with intrinsic spin-orbit coupling by selectively doping two regions creating a potential step. For a clean graphene ribbon, the transmission of the topological edge states through a n-n or p-p junction is perfect irrespective of the ribbon termination, width, and potential step parameters due to the orthogonality of incoming and outgoing edge channels. This is shown numerically for an arbitrary crystallographic orientation of the ribbon and proven analytically for zigzag and metallic armchair boundary conditions. In disordered ribbons, the orthogonality between left- and right-movers is in general destroyed and backscattering sets in. However, transmission approaches one by increasing the ribbon's width, even in the presence of strong edge roughness.