Spin relaxation mechanism in graphene: resonant scattering by magnetic impurities

TL;DR

This paper proposes that resonant scattering by magnetic impurities, especially hydrogen adatoms, explains the short spin relaxation times observed in graphene, supported by first-principles calculations and a theoretical model.

Contribution

It introduces a resonant scattering mechanism involving magnetic impurities as the cause of rapid spin relaxation in graphene, supported by first-principles and effective Hamiltonian modeling.

Findings

Resonant scattering by magnetic moments accounts for ~100 ps spin relaxation time.

Smearing of resonance peaks by electron-hole puddles matches experimental data.

Hydrogen adatoms are identified as a key source of local magnetic moments.

Abstract

It is proposed that the observed small (100 ps) spin relaxation time in graphene is due to resonant scattering by local magnetic moments. At resonances, magnetic moments behave as spin hot spots: the spin-flip scattering rates are as large as the spin-conserving ones, as long as the exchange interaction is greater than the resonance width. Smearing of the resonance peaks by the presence of electron-hole puddles gives quantitative agreement with experiment, for about 1 ppm of local moments. While the local moments can come from a variety of sources, we specifically focus on hydrogen adatoms. We perform first-principles supercell calculations and introduce an effective Hamiltonian to obtain realistic input parameters for our mechanism.