Spin-Phonon coupling parameters from maximally localized Wannier functions and first principles electronic structure: the case of durene single crystal

Spin-orbit interaction is an important vehicle for spin relaxation. At finite temperature lattice vibrations modulate the spin-orbit interaction and thus generate a mechanism for spin-phonon coupling, which needs to be incorporated in any quantitative analysis of spin transport. Starting from a density functional theory \textit{ab initio} electronic structure, we calculate spin-phonon matrix elements over the basis of maximally localized Wannier functions. Such coupling terms form an effective Hamiltonian to be used to extract thermodynamic quantities, within a multiscale approach particularly suitable for organic crystals. The symmetry of the various matrix elements are analyzed by using the $\Gamma$-point phonon modes of a one-dimensional chain of Pb atoms. Then the method is employed to extract the spin-phonon coupling of solid durene, a high-mobility crystal organic semiconducting. Owing to the small masses of carbon and hydrogen spin-orbit is weak in durene and so is the spin-phonon coupling. Most importantly we demonstrate that the largest contribution to the spin-phonon interaction originates from Holstein-like phonons, namely from internal molecular vibrations

Origin of the n-type and p-type conductivity of MoS2 monolayers on a SiO2 substrate

Ab-initio density functional theory calculations are performed to study the electronic properties of a MoS2 monolayer deposited over a SiO2 substrate in the presence of interface impurities and defects. When MoS2 is placed on a defect-free substrate the oxide plays an insignificant role, since the conduction band top and the valence band minimum of MoS2 are located approximately in the middle of the SiO2 band-gap. However, if Na impurities and O dangling bonds are introduced at the SiO2 surface, these lead to localized states, which modulate the conductivity of the MoS2 monolayer from n- to p-type. Our results show that the conductive properties of MoS2 deposited on SiO2 are mainly determined by the detailed structure of the MoS2 /SiO2 interface, and suggest that doping the substrate can represent a viable strategy for engineering MoS2 -based devices.Comment: 8 pages, 7 figure

MgN: a new promising material for spintronic applications

Density functional theory calculations demonstrate that rocksalt MgN is a magnetic material at the verge of half-metallicity, with an electronic structure robust against strong correlations and spin-orbit interaction. Furthermore the calculated heat of formation describes the compound as metastable and suggests that it can be fabricated by tuning the relative Mg and N abundance during growth. Intriguingly the equilibrium lattice constant is close to that of MgO, so that MgN is likely to form as an inclusion during the fabrication of N-doped MgO. We then speculate that the MgO/MgN system may represent a unique materials platform for magnetic tunnel junctions not incorporating any transition metals

Spin-flip inelastic electron tunneling spectroscopy in atomic chains

We present a theoretical study of the spin transport properties of mono-atomic magnetic chains with a focus on the spectroscopical features of the I-V curve associated to spin-flip processes. Our calculations are based on the s-d model for magnetism with the electron transport treated at the level of the non-equilibrium Green's function formalism. Inelastic spin-flip scattering processes are introduced perturbatively via the first Born approximation and an expression for the associated self-energy is derived. The computational method is then applied to describe the I-V characteristics and its derivatives of one dimensional chains of Mn atoms and the results are then compared to available experimental data. We find a qualitative and quantitative agreement between the calculated and the experimental conductance spectra. Significantly we are able to describe the relative intensities of the spin excitation features in the I-V curve, by means of a careful analysis of the spin transition selection rules associated to the atomic chains