Nonlocal topological valley transport at large valley Hall angles

TL;DR

This paper explains the saturation of nonlocal resistance in high-quality gapped graphene by showing it results from bulk topological transport at large valley Hall angles, transitioning from a power-law to a constant behavior.

Contribution

It demonstrates that the saturation of nonlocal resistance is compatible with bulk topological transport in the regime of large valley Hall angles, clarifying experimental observations.

Findings

Nonlocal resistance dependence weakens with increasing valley Hall angles.

Transition from $ ho^3_{c, xx}$ power-law to $ ho$-independent behavior.

Saturation explained by bulk topological transport at large VHAs.

Abstract

Berry curvature hot spots in two-dimensional materials with broken inversion symmetry are responsible for the existence of transverse valley currents, which give rise to giant nonlocal dc voltages. Recent experiments in high-quality gapped graphene have highlighted a saturation of the nonlocal resistance as a function of the longitudinal charge resistivity $\rho_{{\rm c}, xx}$, when the system is driven deep into the insulating phase. The origin of this saturation is, to date, unclear. In this work we show that this behavior is fully compatible with bulk topological transport in the regime of large valley Hall angles (VHAs). We demonstrate that, for a fixed value of the valley diffusion length, the dependence of the nonlocal resistance on $\rho_{{\rm c}, xx}$ weakens for increasing VHAs, transitioning from the standard $\rho^3_{{\rm c}, xx}$ power-law to a result that is independent of $\rho_{{\rm c}, xx}$.