1,109 research outputs found
Drag Force, Jet Quenching, and AdS/QCD
In this note, two important transport observables in the RHIC experiment,
relaxation time constant and jet quenching parameter, are calculated from an
AdS/QCD model. A quark moving in the viscous medium such as the
Quark-Gluon-Plasma is modelled by an open string whose end point travels on the
boundary of a deformed AdS_5 black hole. The correction introduced via the
deformed AdS_5 is believed to help us better understand the data which is
expected to be measured in the RHIC.Comment: 13 pages, 4 figures, revised for PRD. Some comments have been added
below Eq.(34) to avoid a misreading in comparison between our result and
CFT'
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
Continuous Generation of Spinmotive Force in a Patterned Ferromagnetic Film
We study, both experimentally and theoretically, the generation of a dc
spinmotive force. By exciting a ferromagnetic resonance of a comb-shaped
ferromagnetic thin film, a continuous spinmotive force is generated.
Experimental results are well reproduced by theoretical calculations, offering
a quantitative and microscopic understanding of this spinmotive force.Comment: 4 pages, 4 figures, accepted to Physical Review Letter
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
Supersymmetry, homology with twisted coefficients and n-dimensional knots
Let be any natural number. Let be any -dimensional knot in
. We define a supersymmetric quantum system for with the following
properties. We firstly construct a set of functional spaces (spaces of
fermionic \{resp. bosonic\} states) and a set of operators (supersymmetric
infinitesimal transformations) in an explicit way. Thus we obtain a set of the
Witten indexes for . Our Witten indexes are topological invariants for
-dimensional knots. Our Witten indexes are not zero in general. If is
equivalent to the trivial knot, all of our Witten indexes are zero. Our Witten
indexes restrict the Alexander polynomials of -knots. If one of our Witten
indexes for an -knot is nonzero, then one of the Alexander polynomials
of is nontrivial. Our Witten indexes are connected with homology with
twisted coefficients. Roughly speaking, our Witten indexes have path integral
representation by using a usual manner of supersymmetric theory.Comment: 10pages, no figure
A p-type Heusler compound: Growth, structure, and properties of epitaxial thin NiYBi films on MgO(100)
Epitaxial semiconducting NiYBi thin films were directly prepared on MgO(100)
substrates by magnetron sputtering. The intensity ratio of the (200) and (400)
diffraction peaks, I(200)/I(400) = 2.93, was close to the theoretical value
(3.03). The electronic structure of NiYBi was calculated using WIEN2k and a
narrow indirect band gap of width 210 meV was found. The valence band spectra
of the films obtained by linear dichroism in hard X-ray photoelectron
spectroscopy exhibit clear structures that are in good agreement with the
calculated band structure of NiYBi
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
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