Spin-orbit coupling in fluorinated graphene

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 × 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 σ 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.

Role of direct exchange and Dzyaloshinskii-Moriya interactions in magnetic properties of graphene derivatives: C2F and C2HМазуренко1, Руденко2, Nikolaev3 et al. 2016Phys. Rev. B602460View full textAdd to dashboardCite

“…The previous first-principles studies [21,22] have demonstrated an enhancement of spin-orbit coupling in C 2 F compared to C 2 H. Here we confirm this finding by calculating the hopping integrals with spin-orbit coupling and estimating the Dzyaloshinskii-Moriya interactions.…”

“…This requires the construction and solution of the model electronic or spin Hamiltonians, which have been only marginally addressed in the literature [17][18][19]. Considerable nonlocal Coulomb correlations typical to graphene [20] and spin-orbit coupling [21,22] complicate the consideration significantly. Finally, practically important aspects such as the role of temperature and external fields in the evolution of magnetic states also remain unclear.…”

Direct coupling between charge current and spin polarization by extrinsic mechanisms in graphene

“…There is also a solid body of theoretical [11][12][13][14] and experimental [15][16][17][18] work indicating that graphene can exhibit strong extrinsic SOC induced by proximity to adatom impurities or metallic substrates. This suggests that graphene-based devices can also play an important role in active spintronics.…”

“…1. Indeed, numerous tight-binding and density functional theory studies have found that adatom impurities induce both types of SOC, with comparable strengths 11,12,14,32,33 .…”

Spin Relaxation Mechanism in Graphene: Resonant Scattering by Magnetic Impurities

“…We plot the ratio R soc ðEÞ of spin-flip versus spin-conserving probabilities R soc ðEÞ¼½jγ σ;σ j 2 þjβ σ;σ j 2 =½jγ σ;σ j 2 þjβ σ;σ j 2 for different values of spin-orbit coupling strength λ=t in the resonant limit, i.e., when U ≫ t. Numerical values of λ=t ¼ 0.001, 0.05, 0.5, taken to compare with Fig. 2, roughly correspond to hydrogenated graphene [29,39], fluorinated graphene [42], and graphene with thallium [43]. In all three cases there is a pronounced enhancement of spin relaxation close to the resonant energy −2t 2 =U.…”