Pseudospin-driven spin relaxation mechanism in graphene

TL;DR

This paper uncovers a unique spin relaxation mechanism in graphene driven by pseudospin entanglement with spin, explaining rapid dephasing and its dependence on charge density, which is distinct from conventional mechanisms.

Contribution

It introduces a novel spin relaxation process in graphene caused by random SOC-induced spin-pseudospin entanglement, unifying experimental observations.

Findings

Fast spin dephasing near the Dirac point

Relaxation times increase away from the Dirac point

Spin relaxation driven by pseudospin entanglement with SOC

Abstract

The possibility of transporting spin information over long distances in graphene, owing to its small intrinsic spin-orbit coupling (SOC) and the absence of hyperfine interaction, has led to intense research into spintronic applications. However, measured spin relaxation times are orders of magnitude smaller than initially predicted, while the main physical process for spin dephasing and its charge-density and disorder dependences remain unconvincingly described by conventional mechanisms. Here, we unravel a spin relaxation mechanism for nonmagnetic samples that follows from an entanglement between spin and pseudospin driven by random SOC, which makes it unique to graphene. The mixing between spin and pseudospin-related Berry's phases results in fast spin dephasing even when approaching the ballistic limit, with increasing relaxation times away from the Dirac point, as observed experimentally. The SOC can be caused by adatoms, ripples or even the substrate, suggesting novel spin manipulation strategies based on the pseudospin degree of freedom.