Valley separation in graphene by polarized light

TL;DR

This paper demonstrates that polarized light can induce a pure valley current in graphene, with the current's direction and magnitude depending on light polarization and electron interactions.

Contribution

It reveals a novel mechanism for valley current generation in graphene using polarized optical excitation, including the role of electron-electron scattering.

Findings

Valley current depends on light polarization and incident angle.

Electron-electron interactions can dominate valley current.

Valley current exhibits opposite directions for orthogonal polarizations.

Abstract

We show that the optical excitation of graphene with polarized light leads to the pure valley current where carriers in the valleys counterflow. The current in each valley originates from asymmetry of optical transitions and electron scattering by impurities owing to the warping of electron energy spectrum. The valley current has strong polarization dependence, its direction is opposite for normally incident beams of orthogonal linear polarizations. In undoped graphene on a substrate with high susceptibility, electron-electron scattering leads to an additional contribution to the valley current that can dominate.