Theory of Nonlocal Transport from Nonlinear Valley Responses

Abstract

We develop a theory for the nonlocal measurement of nonlinear valley Hall effect. Different from the linear case where the direct and the inverse processes are reciprocal, we unveil that the nonlinear inverse valley Hall effect needed to generate nonlocal voltage signal must have a distinct symmetry character and involve distinct mechanisms compared to the nonlinear valley Hall response it probes. Particularly, it must be valley-even, in contrast to both linear and nonlinear valley Hall effects which are valley-odd. Layer groups that permit such nonlocal valley responses are obtained via symmetry analysis, and formulas for the nonlocal signals are derived. In the presence of both linear and nonlinear valley responses, we show that the different responses can be distinguished by their distinct scaling behaviors in the different harmonic components, under a low-frequency ac driving. Combined with first-principles calculations, we predict sizable nonlocal transport signals from nonlinear valley responses in bilayer $T_{d}$-WTe$_{2}$. Our work lays a foundation for nonlocal transport studies on the emerging nonlinear valleytronics.

Figures (2)

• Figure 1: Schematic of nonlocal measurement setup. The sample strip has a width $w$. A current $I$ is applied between contacts 1 and 2, and the voltage signal between 3 and 4 is measured.
• Figure 2: (a) Crystal structure and (b) calculated low-energy band structure of bilayer $T_{d}$-WTe$_{2}$. (c) The Fermi surface at chemical potential of 40 meV, corresponding to the two valleys $Q$ and $Q^{\prime}$ connected by mirror symmetry. (d) Calculated intrinsic linear and nonlinear valley Hall conductivities versus chemical potential $\mu$.