Contacts and upstream modes explain the electron-hole asymmetry in the graphene quantum Hall regime

TL;DR

This paper investigates the electron-hole asymmetry in graphene's quantum Hall effect, revealing that upstream modes and local doping near contacts cause different breakdown behaviors for electrons and holes.

Contribution

It introduces a new understanding of electron-hole asymmetry by linking upstream modes and local doping to the observed transport differences in graphene.

Findings

Upstream modes influence electron-hole asymmetry.

Local doping near contacts affects quantum Hall breakdown.

Different topological breakdown mechanisms for electrons and holes.

Abstract

Observations of electron-hole asymmetry in transport through graphene devices at high magnetic field challenge prevalent models of the graphene quantum Hall effect. Here, we study this asymmetry both in conventional magnetotransport and in scanning gate microscopy maps measured in an encapsulated graphene constriction. We reveal that the presence of upstream modes and local doping in the vicinity of electrical contacts leads to a totally different picture of topological breakdown for electrons and holes, explaining the observed asymmetry.