Impact of novel electron-phonon coupling mechanisms on valley physics in two-dimensional materials

TL;DR

This paper investigates how different electron-phonon coupling mechanisms influence valley transport in 2D materials, revealing conditions for valley Hall effects and potential for tunable valley acoustoelectronics.

Contribution

It provides a systematic analysis of various electron-phonon couplings and their distinct impacts on valley physics, including the effects of strain and Fermi velocity variations.

Findings

Dirac cone tilt and deformation potential have similar valley Hall responses.

Position-dependent Fermi velocity coupling behaves differently, affecting valley transport.

Nonuniform strain can completely suppress valley Hall effects.

Abstract

We systematically study the impact of various electron-acoustic-phonon coupling mechanisms on valley physics in two-dimensional materials. In the static strain limit, we find that Dirac cone tilt and deformation potential have analogous valley Hall response since they fall into the same universality class of pseudospin structure. However, such argument fails for the coupling mechanism with position-dependent Fermi velocity. For the isotropic case, a significant valley Hall effect occurs near charge neutrality similar to the bond-length change, whereas for the anisotropic case, the geometric valley transport is suppressed, akin to the deformation potential. Gap opening mechanism by nonuniform strain is found to totally inhibit the valley Hall transport, even if the dynamics of strains are introduced. By varying gate voltage, a tunable phonon-assisted valley Hall response can be realized, which paves a way toward rich phenomena and new functionalities of valley acoustoelectronics.