Valley Pumping via Edge States and the Nonlocal Valley Hall Effect in Two-Dimensional Semiconductors

TL;DR

This paper investigates how sample edges influence nonlocal valley Hall signals in 2D semiconductors, revealing edge sensitivity and enhancement effects that challenge the interpretation of bulk intrinsic valley Hall phenomena.

Contribution

It demonstrates that edge electronic structure significantly affects nonlocal valley Hall responses, highlighting the importance of edge effects in interpreting experimental results.

Findings

Edge electronic structure impacts nonlocal valley Hall signals.

Nonlocal response is enhanced when edge conductivity exceeds bulk.

Edge effects can mimic or amplify bulk valley Hall phenomena.

Abstract

Recent experiments have studied the temperature and gate voltage dependence of nonlocal transport in bilayer graphene, identifying features thought to be associated with the two-dimensional semiconductor's bulk intrinsic valley Hall effect. Here, we use both simple microscopic tight-binding ribbon models and phenomenological bulk transport equations to emphasize the impact of sample edges on the nonlocal voltage signals. We show that the nonlocal valley Hall response is sensitive to electronic structure details at the sample edges, and that it is enhanced when the local longitudinal conductivity is larger near the sample edges than in the bulk. We discuss recent experiments in light of these findings and also discuss the close analogy between electron pumping between valleys near two-dimensional sample edges in the valley Hall effect, and bulk pumping between valleys due to the chiral anomaly in three-dimensional topological semimetals.