Spin-orbit coupling in fluorinated graphene

TL;DR

This paper provides a theoretical analysis of spin-orbit coupling effects in fluorinated graphene, revealing that fluorine adatoms induce a giant local spin-orbit coupling primarily due to fluorine's intrinsic properties, with implications for spin transport.

Contribution

The study introduces a realistic effective Hamiltonian for fluorinated graphene and quantifies the dominant role of fluorine's own spin-orbit coupling, contrasting it with hydrogen adatoms.

Findings

Fluorine induces about 10 meV spin-orbit splitting in dense graphene.

The induced spin-orbit coupling is approximately 1000 times greater than in pristine graphene.

Fluorine adatoms are weakly resonant scatterers with a broad density of states peak 260 meV below the Dirac point.

Abstract

We report on theoretical investigations of the spin-orbit coupling effects in fluorinated graphene. First-principles density functional calculations are performed for the dense and dilute adatom coverage limits. The dense limit is represented by the single-side semifluorinated graphene, which is a metal with spin-orbit splittings of about 10 meV. To simulate the effects of a single adatom, we also calculate the electronic structure of a $10 \times 10$ supercell, with one fluorine atom in the top position. Since this dilute limit is useful to study spin transport and spin relaxation, we also introduce a realistic effective hopping Hamiltonian, based on symmetry considerations, which describes the supercell bands around the Fermi level. We provide the Hamiltonian parameters which are best fits to the first-principles data. We demonstrate that, unlike for the case of hydrogen adatoms, fluorine's own spin-orbit coupling is the principal cause of the giant induced local spin-orbit coupling in graphene. The $sp^3$ hybridization induced transfer of spin-orbit coupling from graphene's $\sigma$ bonds, important for hydrogenated graphene, contributes much less. Furthermore, the magnitude of the induced spin-orbit coupling due to fluorine adatoms is about $1000$ times more than that of pristine graphene, and 10 times more than that of hydrogenated graphene. Also unlike hydrogen, the fluorine adatom is not a narrow resonant scatterer at the Dirac point. The resonant peak in the density of states of fluorinated graphene in the dilute limit lies 260 meV below the Dirac point. The peak is rather broad, about 300 meV, making the fluorine adatom only a weakly resonant scatterer.