Valley Hall Effect and Non-Local Resistance in Locally Gapped Graphene

TL;DR

This paper demonstrates how spatially varying sublattice symmetry breaking in graphene induces bulk valley-polarized currents, revealing a valley Hall effect through non-local resistance measurements, with implications for valleytronics and electron optics.

Contribution

It introduces a novel mechanism for valley Hall effect in graphene via non-uniform bandgaps, supported by quantum transport simulations and experimental interpretation.

Findings

Bulk valley-polarized currents are driven by local bandgap variations.

Non-local resistance fingerprints reveal valley-dependent scattering.

The effects are robust against disorder and explain previous experimental controversies.

Abstract

We report on the emergence of bulk, valley-polarized currents in graphene-based devices, driven by spatially varying regions of broken sublattice symmetry, and revealed by non-local resistance ($R_\mathrm{NL}$) fingerprints. By using a combination of quantum transport formalisms, giving access to bulk properties as well as multi-terminal device responses, the presence of a non-uniform local bandgap is shown to give rise to valley-dependent scattering and a finite Fermi surface contribution to the valley Hall conductivity, related to characteristics of $R_\mathrm{NL}$. These features are robust against disorder and provide a plausible interpretation of controversial experiments in graphene/hBN superlattices. Our findings suggest both an alternative mechanism for the generation of valley Hall effect in graphene, and a route towards valley-dependent electron optics, by materials and device engineering.