2,312 research outputs found
On weighted structured total least squares
In this contribution we extend the result of (Markovsky et. al, SIAM J. of Matrix Anal. and Appl., 2005) to the case of weighted cost function. It is shown that the computational complexity of the proposed algorithm is preserved linear in the sample size when the weight matrix is banded with bandwidth that is independent of the sample size
Circular photon drag effect in bulk tellurium
The circular photon drag effect is observed in a bulk semiconductor. The
photocurrent caused by a transfer of both translational and angular momenta of
light to charge carriers is detected in tellurium in the mid-infrared frequency
range. Dependencies of the photocurrent on the light polarization and on the
incidence angle agree with the symmetry analysis of the circular photon drag
effect. Microscopic models of the effect are developed for both intra- and
inter-subband optical absorption in the valence band of tellurium. The shift
contribution to the circular photon drag current is calculated. An observed
decrease of the circular photon drag current with increase of the photon energy
is explained by the theory for inter-subband optical transitions. Theoretical
estimates of the circular photon drag current agree with the experimental data.Comment: 8 pages, 4 figure
Separable states can be used to distribute entanglement
We show that no entanglement is necessary to distribute entanglement; that
is, two distant particles can be entangled by sending a third particle that is
never entangled with the other two. Similarly, two particles can become
entangled by continuous interaction with a highly mixed mediating particle that
never itself becomes entangled. We also consider analogous properties of
completely positive maps, in which the composition of two separable maps can
create entanglement.Comment: 4 pages, 2 figures. Slight modification
Interaction-assisted propagation of Coulomb-correlated electron-hole pairs in disordered semiconductors
A two-band model of a disordered semiconductor is used to analyze dynamical
interaction induced weakening of localization in a system that is accessible to
experimental verification. The results show a dependence on the sign of the
two-particle interaction and on the optical excitation energy of the
Coulomb-correlated electron-hole pair.Comment: 4 pages and 3 ps figure
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
Valley separation in graphene by polarized light
We show that the optical excitation of graphene with polarized light leads to
the pure valley current where carriers in the valleys counterflow. The current
in each valley originates from asymmetry of optical transitions and electron
scattering by impurities owing to the warping of electron energy spectrum. The
valley current has strong polarization dependence, its direction is opposite
for normally incident beams of orthogonal linear polarizations. In undoped
graphene on a substrate with high susceptibility, electron-electron scattering
leads to an additional contribution to the valley current that can dominate.Comment: 4+ pages, 2 figure
Off-diagonal disorder in the Anderson model of localization
We examine the localization properties of the Anderson Hamiltonian with
additional off-diagonal disorder using the transfer-matrix method and
finite-size scaling. We compute the localization lengths and study the
metal-insulator transition (MIT) as a function of diagonal disorder, as well as
its energy dependence. Furthermore we investigate the different influence of
odd and even system sizes on the localization properties in quasi
one-dimensional systems. Applying the finite-size scaling approach in
conjunction with a nonlinear fitting procedure yields the critical parameters
of the MIT. In three dimensions, we find that the resulting critical exponent
of the localization length agrees with the exponent for the Anderson model with
pure diagonal disorder.Comment: 12 pages including 4 EPS figures, accepted for publication in phys.
stat. sol. (b
UCN Upscattering rates in a molecular deuterium crystal
A calculation of ultra-cold neutron (UCN) upscattering rates in molecular
deuterium solids has been carried out, taking into account intra-molecular
exictations and phonons. The different moelcular species ortho-D2 (with even
rotational quantum number J) and para-D2 (with odd J) exhibit significantly
different UCN-phonon annihilation cross-sections. Para- to ortho-D2 conversion,
furthermore, couples UCN to an energy bath of excited rotational states without
mediating phonons. This anomalous upscattering mechanism restricts the UCN
lifetime to 4.6 msec in a normal-D2 solid with 33% para content.Comment: 3 pages, one figur
Giant Spin Relaxation Anisotropy in Zinc-Blende Heterostructures
Spin relaxation in-plane anisotropy is predicted for heterostructures based
on zinc-blende semiconductors. It is shown that it manifests itself especially
brightly if the two spin relaxation mechanisms (D'yakonov-Perel' and Rashba)
are comparable in efficiency. It is demonstrated that for the quantum well
grown along the [0 0 1] direction, the main axes of spin relaxation rate tensor
are [1 1 0] and [1 -1 0].Comment: 3 pages, NO figure
Weak localization of holes in high-mobility heterostructures
Theory of weak localization is developed for two-dimensional holes in
semiconductor heterostructures. Ballistic regime of weak localization where the
backscattering occurs from few impurities is studied with account for
anisotropic momentum scattering of holes. The transition from weak localization
to anti-localization is demonstrated for long dephasing times. For stronger
dephasing the conductivity correction is negative at all hole densities due to
non-monotonous dependence of the spin relaxation time on the hole wavevector.
The anomalous temperature dependent correction to the conductivity is
calculated. We show that the temperature dependence of the conductivity is
non-monotonous at moderate hole densities.Comment: 5 pages, 4 figure
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