Gate induced enhancement of spin-orbit coupling in dilute fluorinated graphene

TL;DR

This study reveals that fluorine adatoms' atomic spin-orbit coupling dominates in fluorinated graphene, and that doping levels significantly modulate SOC strength, offering a way to control spin relaxation.

Contribution

It demonstrates that fluorine's atomic SOC, not lattice distortion, is the main source of SOC in fluorinated graphene, and models doping effects on SOC.

Findings

SOC is mainly due to fluorine atomic spin-orbit coupling.

Electron doping enhances SOC, hole doping reduces it.

Doping can tune spin relaxation in fluorinated graphene.

Abstract

We analyze the origin of spin-orbit coupling (SOC) in fluorinated graphene using Density Functional Theory (DFT) and a tight-binding model for the relevant orbitals. As it turns out, the dominant source of SOC is the atomic spin-orbit of fluorine adatoms and not the impurity induced SOC based on the distortion of the graphene plane as in hydrogenated graphene. More interestingly, our DFT calculations show that SOC is strongly affected by both the type and concentrations of the graphene's carriers, being enhanced by electron doping and reduced by hole doping. This effect is due to the charge transfer to the fluorine adatom and the consequent change in the fluorine-carbon bonding. Our simple tight-binding model, that includes the SOC of the $2p$ orbitals of F and effective parameters based on maximally localized Wannier functions, is able to account for the effect. The strong enhancement of the SOC induced by graphene doping opens the possibility to tune the spin relaxation in this material.