1,698 research outputs found
Interface engineering of graphene nanosheet reinforced ZrB 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 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
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 - 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
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
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 -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
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