Spin Transport in Hydrogenated Graphene

TL;DR

This review explores how hydrogenation affects spin transport in graphene, highlighting the roles of spin-orbit coupling, local magnetism, and impurity density in determining spin lifetimes and relaxation mechanisms.

Contribution

It provides a comprehensive theoretical analysis of spin relaxation mechanisms in hydrogenated graphene, integrating first-principles calculations with models of magnetic scattering and impurity effects.

Findings

Spin lifetimes around 1 nanosecond at 1 ppm hydrogen impurities

Scaling of spin lifetimes follows the Elliott-Yafet mechanism

Magnetism significantly contributes to spin polarization loss in ultraclean graphene

Abstract

In this review we discuss the multifaceted problem of spin transport in hydrogenated graphene from a theoretical perspective. The current experimental findings suggest that hydrogenation can either increase or decrease spin lifetimes, which calls for clarification. We first discuss the spin-orbit coupling induced by local $\sigma-\pi$ re-hybridization and ${\bf sp}^{3}$ C-H defect formation together with the formation of a local magnetic moment. First-principles calculations of hydrogenated graphene unravel the strong interplay of spin-orbit and exchange couplings. The concept of magnetic scattering resonances, recently introduced \cite{Kochan2014} is revisited by describing the local magnetism through the self-consistent Hubbard model in the mean field approximation in the dilute limit, while spin relaxation lengths and transport times are computed using an efficient real space order N wavepacket propagation method. Typical spin lifetimes on the order of 1 nanosecond are obtained for 1 ppm of hydrogen impurities (corresponding to transport time about 50 ps), and the scaling of spin lifetimes with impurity density is described by the Elliott-Yafet mechanism. This reinforces the statement that magnetism is the origin of the substantial spin polarization loss in the ultraclean graphene limit.