Valley current in graphene through electron-phonon interaction

TL;DR

This paper explores how electron-phonon interactions in graphene induce a valley current, which depends on chirality and occurs without breaking spatial inversion symmetry, increasing with temperature.

Contribution

It reveals a novel mechanism for valley current generation in graphene via electron-phonon collisions that mix scalar and vector vertices, independent of inversion symmetry breaking.

Findings

Valley current arises from electron-phonon collision integral effects.

The valley current increases with temperature due to higher phonon collision rates.

Detection possible through nonlocal electric current measurements.

Abstract

We discuss valley current, which is carried by quasiparticles in graphene. We show that the valley current arises owing to a peculiar term in the electron-phonon collision integral that mixes the scalar and vector gauge-field-like vertices in the electron-phonon interaction. This mixing makes collisions of phonons with electrons sensitive to their chirality, which is opposite in two valleys. As a result of collisions with phonons, electrons of the different valleys deviate in opposite directions. Breaking the spatial inversion symmetry is not needed for a valley-dependent deviation of the quasiparticle current. The effect exists both in pristine graphene or bilayer graphene samples, and it increases with temperature owing to a higher rate of collisions with phonons at higher temperatures. The valley current carried by quasiparticles could be detected by measuring the electric current using a nonlocal transformer of a suitable design.