13,237 research outputs found
Some symmetry properties of spin currents and spin polarizations in multi-terminal mesoscopic spin-orbit coupled systems
We study theoretically some symmetry properties of spin currents and spin
polarizations in multi-terminal mesoscopic spin-orbit coupled systems. Based on
a scattering wave function approach, we show rigorously that in the equilibrium
state no finite spin polarizations can exist in a multi-terminal mesoscopic
spin-orbit coupled system (both in the leads and in the spin-orbit coupled
region) and also no finite equilibrium terminal spin currents can exist. By use
of a typical two-terminal mesoscopic spin-orbit coupled system as the example,
we show explicitly that the nonequilibrium terminal spin currents in a
multi-terminal mesoscopic spin-orbit coupled system are non-conservative in
general. This non-conservation of terminal spin currents is not caused by the
use of an improper definition of spin current but is intrinsic to
spin-dependent transports in mesoscopic spin-orbit coupled systems. We also
show that the nonequilibrium lateral edge spin accumulation induced by a
longitudinal charge current in a thin strip of \textit{finite} length of a
two-dimensional electronic system with intrinsic spin-orbit coupling may be
non-antisymmetric in general, which implies that some cautions may need to be
taken when attributing the occurrence of nonequilibrium lateral edge spin
accumulation induced by a longitudinal charge current in such a system to an
intrinsic spin Hall effect.Comment: 11 pages, 6 figure
Temperature Profiles of Accretion Disks around Rapidly Rotating Neutron Stars in General Relativity and Implications for Cygnus X-2
We calculate the temperature profiles of (thin) accretion disks around
rapidly rotating neutron stars (with low surface magnetic fields), taking into
account the full effects of general relativity. We then consider a model for
the spectrum of the X-ray emission from the disk, parameterized by the mass
accretion rate, the color temperature and the rotation rate of the neutron
star. We derive constraints on these parameters for the X-ray source Cygnus X-2
using the estimates of the maximum temperature in the disk along with the disk
and boundary layer luminosities, using the spectrum inferred from the EXOSAT
data. Our calculations suggest that the neutron star in Cygnus X-2 rotates
close to the centrifugal mass-shed limit. Possible constraints on the neutron
star equation of state are also discussed.Comment: 18 pages, 9 figs., 2 tables, uses psbox.tex and emulateapj5.sty.
Submitted to Ap
Non-equilibrium spin polarization effects in spin-orbit coupling system and contacting metallic leads
We study theoretically the current-induced spin polarization effect in a
two-terminal mesoscopic structure which is composed of a semiconductor
two-dimensional electron gas (2DEG) bar with Rashba spin-orbit (SO) interaction
and two attached ideal leads. The nonequilibrium spin density is calculated by
solving the scattering wave functions explicitly within the ballistic transport
regime. We found that for a Rashba SO system the electrical current can induce
spin polarization in the SO system as well as in the ideal leads. The induced
polarization in the 2DEG shows some qualitative features of the intrinsic spin
Hall effect. On the other hand, the nonequilibrium spin density in the ideal
leads, after being averaged in the transversal direction, is independent of the
distance measured from the lead/SO system interface, except in the vicinity of
the interface. Such a lead polarization effect can even be enhanced by the
presence of weak impurity scattering in the SO system and may be detectable in
real experiments.Comment: 6 pages,5 figure
Brans-Dicke theory: Jordan vs Einstein Frame
It is well known that, in contrast to general relativity, there are two
conformally related frames, the Jordan frame and the Einstein frame, in which
the Brans-Dicke theory, a prototype of generic scalar-tensor theory, can be
formulated. There is a long standing debate on the physical equivalence of the
formulations in these two different frames. It is shown here that gravitational
deflection of light to second order accuracy may observationally distinguish
the two versions of the Brans-Dicke theory.Comment: 10 pages, Accepted by Mod. Phys. Letts.
Conductance calculations for quantum wires and interfaces: mode matching and Green functions
Landauer's formula relates the conductance of a quantum wire or interface to
transmission probabilities. Total transmission probabilities are frequently
calculated using Green function techniques and an expression first derived by
Caroli. Alternatively, partial transmission probabilities can be calculated
from the scattering wave functions that are obtained by matching the wave
functions in the scattering region to the Bloch modes of ideal bulk leads. An
elegant technique for doing this, formulated originally by Ando, is here
generalized to any Hamiltonian that can be represented in tight-binding form. A
more compact expression for the transmission matrix elements is derived and it
is shown how all the Green function results can be derived from the mode
matching technique. We illustrate this for a simple model which can be studied
analytically, and for an Fe|vacuum|Fe tunnel junction which we study using
first-principles calculations.Comment: 14 pages, 5 figure
Nonlinear Transport of Bose-Einstein Condensates Through Waveguides with Disorder
We study the coherent flow of a guided Bose-Einstein condensate incident over
a disordered region of length L. We introduce a model of disordered potential
that originates from magnetic fluctuations inherent to microfabricated guides.
This model allows for analytical and numerical studies of realistic transport
experiments. The repulsive interaction among the condensate atoms in the beam
induces different transport regimes. Below some critical interaction (or for
sufficiently small L) a stationary flow is observed. In this regime, the
transmission decreases exponentially with L. For strong interaction (or large
L), the system displays a transition towards a time dependent flow with an
algebraic decay of the time averaged transmission.Comment: 15 pages, 9 figure
Characteristic slepton signal in anomaly mediated SUSY breaking models via gauge boson fusion at the LHC
We point out that slepton pairs produced via gauge boson fusion in anomaly
mediated supersymmetry breaking (AMSB) model have very characteristic and
almost clean signal at the Large Hadron Collider. In this article, we discuss
how one lepton associated with missing energy and produced in between two
high- and high-mass forward jets can explore quite heavy sleptons in this
scenario.Comment: Version to appear in Physical Review
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