Valley Hall Effect and Nonlocal Transport in Strained Graphene

TL;DR

This paper demonstrates that modest strain in graphene induces a classical valley Hall effect detectable via nonlocal transport, supported by a theoretical framework based on the quantum Boltzmann equation.

Contribution

It introduces a theory for strain-induced valley Hall effect in graphene, accounting for impurity averaging and providing predictions for nonlocal resistance measurements.

Findings

Strain in graphene can produce a detectable valley Hall effect.

The theory predicts nonlocal resistance in diffusive graphene devices.

Impurity averaging destroys quantum coherence, simplifying the transport model.

Abstract

Graphene subject to high levels of shear strain leads to strong pseudo-magnetic fields resulting in the emergence of Landau levels. Here we show that, with modest levels of strain, graphene can also sustain a classical valley hall effect (VHE) that can be detected in nonlocal transport measurements. We provide a theory of the strain-induced VHE starting from the quantum Boltzmann equation. This allows us to show that, averaging over short-range impurity configurations destroys quantum coherence between valleys, leaving the elastic scattering time and inter-valley scattering rate as the only parameters characterizing the transport theory. Using the theory, we compute the nonlocal resistance of a Hall bar device in the diffusive regime. Our theory is also relevant for the study of moderate strain effects in the (nonlocal) transport properties of other two-dimensional materials and van der Walls heterostructures.