Nonlinear valley Hall effect in a bilayer transition metal dichalcogenide

TL;DR

This paper demonstrates that nonlinear valley Hall effects can be realized in bilayer transition metal dichalcogenides like MoS₂ through strain-induced band tilts, expanding valleytronic material options and device possibilities.

Contribution

It reveals nonlinear valley Hall transport in bilayer TMDs driven by strain, using models and calculations, despite centrosymmetry in bilayers.

Findings

Nonlinear valley Hall conductivities emerge in strained MoS₂ bilayers.

Conductivities are highly tunable via strain, chemical potential, and interlayer gap.

Strain-induced band tilts enable valley-contrasting transport in centrosymmetric bilayers.

Abstract

Valley-contrasting Hall transport conventionally relies on the inversion symmetry breaking in two-dimensional systems, which greatly limits the selection range of valley materials. In particular, while monolayer transition metal dichalcogenides have been widely utilized as a well-known class of valley materials in valleytronics, the centrosymmetric nature hinders the realization of valley-contrasting properties in the bilayer counterparts. Here, taking MoS$_{2}$ as an example, we discover valley-contrasting transport in bilayer transition metal dichalcogenides by exploring nonlinear transport regime. Using effective models and first-principles calculations, our work demonstrates that nonvanishing nonlinear valley Hall conductivities emerge in a uniaxially strained MoS$_{2}$ bilayer, owing to strain-induced band tilts of Dirac fermions. With the aid of small spin-orbit-coupling induced band splittings, the conduction bands generate much remarkable nonlinear valley Hall conductivity. Moreover, the nonlinear conductivities are highly tunable through modulating the strength and the direction of the strain, chemical potential, and interlayer gap. Our findings not only expands material choices for valleytronic applications, but also provides opportunities for designing advanced electronic devices that leverage nonlinear valley transports.