Direct coupling between charge current and spin polarization by extrinsic mechanisms in graphene

TL;DR

This paper develops a comprehensive theory of spin transport in graphene with extrinsic spin-orbit coupling, revealing a new anisotropic spin precession process that enhances current-induced spin polarization, aiding spintronic device design.

Contribution

It introduces a novel theoretical framework including spin precession during scattering and identifies a new anisotropic spin precession mechanism specific to 2D graphene with extrinsic SOC.

Findings

Identification of anisotropic spin precession scattering in graphene.

Both Elliott-Yafet and Dyakonov-Perel relaxation mechanisms are significant.

The Dyakonov-Perel mechanism can dominate under certain conditions.

Abstract

Spintronics---the all-electrical control of the electron spin for quantum or classical information storage and processing---is one of the most promising applications of the two-dimensional material graphene. Although pristine graphene has negligible spin-orbit coupling (SOC), both theory and experiment suggest that SOC in graphene can be substantially enhanced by extrinsic means, such as functionalization by adatom impurities. We present a theory of transport in graphene that accounts for the full spin-coherent dynamics of the carriers, including hitherto-neglected spin precession processes during resonant scattering with dilute impurities. We identify a novel "anisotropic spin precession scattering" process, specific to two dimensions and extrinsic SOC, which contributes to a large current-induced spin polarization in graphene. The theory also yields a comprehensive description of the spin relaxation mechanisms in impurity-decorated graphene: the Elliot-Yafet and Dyakonov-Perel relaxation rates are both present, and we find that the latter can dominate for some choices of carrier density and impurity strength. This provides theoretical foundations for designing future graphene-based integrated spintronic devices.