Spin-valley collective modes of the electron liquid in graphene

TL;DR

This paper develops a theoretical framework for collective modes in graphene's electron liquid, revealing dominant over-damped valley and spin modes that impact valley- and spintronics applications.

Contribution

It introduces a comprehensive theory of collective modes in graphene's Fermi liquid, including valley and spin imbalance modes, with detailed interaction and relaxation rate analysis.

Findings

All modes but the plasmon are over-damped under realistic conditions.

Identifies valley and spin imbalance modes with specific symmetry properties.

Provides fundamental constraints on graphene valley- and spintronics applications.

Abstract

We develop the theory of collective modes supported by a Fermi liquid of electrons in pristine graphene. Under reasonable assumptions regarding the electron-electron interaction, all the modes but the plasmon are over-damped. In addition to the $SU(2)$ symmetric spin mode, these include also the valley imbalance modes obeying a $U(1)$ symmetry, and a $U(2)$ symmetric valley spin imbalance mode. We derive the interactions and diffusion constants characterizing the over-damped modes. The corresponding relaxation rates set fundamental constraints on graphene valley- and spintronics applications.