666 research outputs found
Ab initio mass tensor molecular dynamics
Mass tensor molecular dynamics was first introduced by Bennett [J. Comput.
Phys. 19, 267 (1975)] for efficient sampling of phase space through the use of
generalized atomic masses. Here, we show how to apply this method to ab initio
molecular dynamics simulations with minimal computational overhead. Test
calculations on liquid water show a threefold reduction in computational effort
without making the fixed geometry approximation. We also present a simple
recipe for estimating the optimal atomic masses using only the first
derivatives of the potential energy.Comment: 19 pages, 5 figure
Theory of magnon-driven spin Seebeck effect
The spin Seebeck effect is a spin-motive force generated by a temperature
gradient in a ferromagnet that can be detected via normal metal contacts
through the inverse spin Hall effect [K. Uchida {\it et al.}, Nature {\bf 455},
778-781 (2008)]. We explain this effect by spin pumping at the contact that is
proportional to the spin-mixing conductance of the interface, the inverse of a
temperature-dependent magnetic coherence volume, and the difference between the
magnon temperature in the ferromagnet and the electron temperature in the
normal metal [D. J. Sanders and D. Walton, Phys. Rev. B {\bf 15}, 1489 (1977)].Comment: 10 pages, 3 figures, 2 tables. This version is NOT the published PRB
but a version with an erratu
Theory of spin Hall magnetoresistance
We present a theory of the spin Hall magnetoresistance (SMR) in multilayers
made from an insulating ferromagnet F, such as yttrium iron garnet (YIG), and a
normal metal N with spin-orbit interactions, such as platinum (Pt). The SMR is
induced by the simultaneous action of spin Hall and inverse spin Hall effects
and therefore a non-equilibrium proximity phenomenon. We compute the SMR in
FN and FNF layered systems, treating N by spin-diffusion theory with
quantum mechanical boundary conditions at the interfaces in terms of the
spin-mixing conductance. Our results explain the experimentally observed spin
Hall magnetoresistance in NF bilayers. For FNF spin valves we predict
an enhanced SMR amplitude when magnetizations are collinear. The SMR and the
spin-transfer torques in these trilayers can be controlled by the magnetic
configuration
Designing evanescent optical interactions to control the expression of Casimir forces in optomechanical structures
We propose an optomechanical structure consisting of a photonic-crystal
(holey) membrane suspended above a layered silicon-on-insulator substrate in
which resonant bonding/antibonding optical forces created by externally
incident light from above enable all-optical control and actuation of stiction
effects induced by the Casimir force. In this way, one can control how the
Casimir force is expressed in the mechanical dynamics of the membrane, not by
changing the Casimir force directly but by optically modifying the geometry and
counteracting the mechanical spring constant to bring the system in or out of
regimes where Casimir physics dominate. The same optical response (reflection
spectrum) of the membrane to the incident light can be exploited to accurately
measure the effects of the Casimir force on the equilibrium separation of the
membrane
QCD Viscosity to Entropy Density Ratio in the Hadronic Phase
Shear viscosity (eta) of QCD in the hadronic phase is computed by the coupled
Boltzmann equations of pions and nucleons in low temperatures and low baryon
number densities. The eta to entropy density ratio eta/s maps out the nuclear
gas-liquid phase transition by forming a valley tracing the phase transition
line in the temperature-chemical potential plane. When the phase transition
turns into a crossover, the eta/s valley gradually disappears. We suspect the
general feature for a first-order phase transition is that eta/s has a
discontinuity in the bottom of the eta/s valley. The discontinuity coincides
with the phase transition line and ends at the critical point. Beyond the
critical point, a smooth eta/s valley is seen. However, the valley could
disappear further away from the critical point. The eta/s measurements might
provide an alternative to identify the critical points.Comment: 16 pages, 4 figures. Minor typos corrected and references adde
Bipolar-Driven Large Magnetoresistance in Silicon
Large linear magnetoresistance (MR) in electron-injected p-type silicon at
very low magnetic field is observed experimentally at room temperature. The
large linear MR is induced in electron-dominated space-charge transport regime,
where the magnetic field modulation of electron-to-hole density ratio controls
the MR, as indicated by the magnetic field dependence of Hall coefficient in
the silicon device. Contrary to the space-charge-induced MR effect in unipolar
silicon device, where the large linear MR is inhomogeneity-induced, our results
provide a different insight into the mechanism of large linear MR in
non-magnetic semiconductors that is not based on the inhomogeneity model. This
approach enables homogeneous semiconductors to exhibit large linear MR at low
magnetic fields that until now has only been appearing in semiconductors with
strong inhomogeneities.Comment: 23 pages, 4 figures (main text), 6 figures (supplemental material
Magmatic contributions to hydrothermal systems
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95694/1/eost9233.pd
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