Observation of Helical Edge States and Fractional Quantum Hall Effect in a Graphene Electron-hole Bilayer

TL;DR

This paper demonstrates a new platform using graphene electron-hole bilayers to realize helical 1d edge conductors with fractional quantum Hall states, enabling studies of nonlocal transport and fractional statistics.

Contribution

It introduces a method to create tunable helical edge states in graphene bilayers combining opposite chiral quantum Hall modes, including fractional regimes.

Findings

Observation of helical edge conductors with suppressed backscattering.

Detection of fractional and integer edge states with opposite chiralities.

Evidence of nonlocal transport signals in the bilayer system.

Abstract

A quantum Hall edge state provides a rich foundation to study electrons in 1-dimension (1d) but is limited to chiral propagation along a single direction. Here, we demonstrate a versatile platform to realize new 1d systems made by combining quantum Hall edge states of opposite chiralities in a graphene electron-hole bilayer. Using this approach, we engineer helical 1d edge conductors where the counterpropagating modes are localized in separate electron and hole layers by a tunable electric field. These helical conductors exhibit strong nonlocal transport signals and suppressed backscattering due to the opposite spin polarizations of the counterpropagating modes. Moreover, we investigate these electron-hole bilayers in the fractional quantum Hall regime, where we observe conduction through fractional and integer edge states of opposite chiralities, paving the way towards the realization of 1d helical systems with fractional quantum statistics.