Microscopic linear response theory of spin relaxation and relativistic transport phenomena in graphene

TL;DR

This paper develops a comprehensive quantum-mechanical framework to analyze spin relaxation and relativistic transport in disordered graphene, capturing key phenomena like charge-spin conversion and spin lifetime relations.

Contribution

It introduces a unified theoretical approach for spin dynamics in disordered Dirac systems, specifically applying it to graphene with Rashba interaction, including diagrammatic evaluation and conservation laws.

Findings

Spin and momentum lifetimes follow Dyakonov-Perel relation.

Spin relaxation rate derived from SU(2) conservation laws.

Framework applicable to both weak and resonant disorder regimes.

Abstract

We present a unified theoretical framework for the study of spin dynamics and relativistic transport phenomena in disordered two-dimensional Dirac systems with pseudospin-spin coupling. The formalism is applied to the paradigmatic case of graphene with uniform Bychkov-Rashba interaction and shown to capture spin relaxation processes and associated charge-to-spin interconversion phenomena in response to generic external perturbations, including spin density fluctuations and electric fields. A controlled diagrammatic evaluation of the generalized spin susceptibility in the diffusive regime of weak spin-orbit interaction allows us to show that the spin and momentum lifetimes satisfy the standard Dyakonov-Perel relation for both weak (Gaussian) and resonant (unitary) nonmagnetic disorder. Finally, we demonstrate that the spin relaxation rate can be derived in the zero-frequency limit by exploiting the SU(2) covariant conservation laws for the spin observables. Our results set the stage for a fully quantum-mechanical description of spin relaxation in both pristine graphene samples with weak spin-orbit fields and in graphene heterostructures with enhanced spin-orbital effects currently attracting much attention.