Interface engineering of graphene nanosheet reinforced ZrB2_2 composites by tuning surface contacts

The mechanical properties of heterophase interfaces are critically important for the behaviour of graphene-reinforced composites. In this work, the structure, adhesion, cleavage and sliding of heterophase interfaces, formed between a ZrB$_2$ matrix and graphene nanosheets, are systematically investigated by density functional theory, and compared to available experimental data. We demonstrate that the surface chemistry of the ZrB$_2$ matrix material largely shapes the interface structures (of either Zr-C-Zr or B-C-B type) and the nature of the interfacial interaction. The Zr-C-Zr interfaces present strong chemical bonding and their response to mechanical stress is significantly influenced by graphene corrugation. In contrast B-C-B interfaces, interacting through the relatively weak $\pi$-$\pi$ stacking, show attributes similar to 2D materials heterostructures. Our theoretical results provide insights into the interface bonding mechanisms in graphene/ceramic composites, and emphasize the prospect for their design via interface engineering enabled by surface contacts

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

Multiprobe quantum spin Hall bars

We analyze electron transport in multiprobe quantum spin Hall (QSH) bars using the B\"{u}ttiker formalism and draw parallels with their quantum Hall (QH) counterparts. We find that in a QSH bar the measured resistance changes upon introducing side voltage probes, in contrast to the QH case. We also study four- and six-terminal geometries and derive the expressions for the resistances. For these our analysis is generalized from the single-channel to the multi-channel case and to the inclusion of backscattering originating from a constriction placed within the bar.Comment: 6 pages, 5 figure