9,376 research outputs found
Derivation of the Lindblad Generator Structure by use of the It\^o Stochastic Calculus
We use the It\^o stochastic calculus to give a simple derivation of the
Lindblad form for the generator of a completely positive density matrix
evolution, by specialization from the corresponding global form for a
completely positive map. As a by-product, we obtain a generalized generator for
a completely positive stochastic density matrix evolution.Comment: Plain TEX, no figures or table
On the weak-coupling limit and complete positivity
We consider two non-interacting systems embedded in a heat bath. If they
remain dynamically independent, physical inconsistencies are avoided only if
the single-system reduced dynamics is completely positive also beyond the
weak-coupling limit.Comment: 11 pages, plain-Te
Onsager relations in a two-dimensional electron gas with spin-orbit coupling
Theory predicts for the two-dimensional electrons gas with only Rashba
spin-orbit interaction a vanishing spin Hall conductivity and at the same time
a finite inverse spin Hall effect. We show how these seemingly contradictory
results are compatible with the Onsager relations: the latter do hold for spin
and particle (charge) currents in the two-dimensional electron gas, although
(i) their form depends on the experimental setup and (ii) a vanishing bulk spin
Hall conductivity does not necessarily imply a vanishing spin Hall effect. We
also discuss the situation in which extrinsic spin orbit from impurities is
present and the bulk spin Hall conductivity can be different from zero.Comment: Accepted versio
Spin polarizations and spin Hall currents in a two-dimensional electron gas with magnetic impurities
We consider a two-dimensional electron gas in the presence of Rashba
spin-orbit coupling, and study the effects of magnetic s-wave impurities and
long-range non-magnetic disorder on the spin-charge dynamics of the system. We
focus on voltage induced spin polarizations and their relation to spin Hall
currents. Our results are obtained using the quasiclassical Green function
technique, and hold in the full range of the disorder parameter .Comment: 5 pages, 2 figures. References added, minor stylistic modification
Spin thermoelectrics in a disordered Fermi gas
We study the connection between the spin-heat and spin-charge response in a
disordered Fermi gas with spin-orbit coupling. It is shown that the ratio
between the above responses can be expressed as the thermopower times a number which depends on the strength and
type of the spin-orbit couplings considered. The general results are
illustrated by examining different two-dimensional electron or hole systems
with different and competing spin-orbit mechanisms, and we conclude that a
metallic system could prove much more efficient as a heat-to-spin than as a
heat-to-charge converter.Comment: 6 pages, 1 figur
Room temperature spin thermoelectrics in metallic films
Considering metallic films at room temperature, we present the first
theoretical study of the spin Nernst and thermal Edelstein effects which takes
into account dynamical spin-orbit coupling, i.e., direct spin-orbit coupling
with the vibrating lattice (phonons) and impurities. This gives rise to two
novel processes, namely a dynamical Elliott-Yafet spin relaxation and a
dynamical side-jump mechanism. Both are the high-temperature counterparts of
the well-known Elliott-Yafet and side-jump, central to the current
understanding of the spin Hall, spin Nernst and Edelstein effects at low .
We consider the experimentally relevant regime , with the Debye
temperature, as the latter is lower than room temperature in transition metals
such as Pt, Au and Ta typically employed in spin injection/extraction
experiments. We show that the interplay between intrinsic (Bychkov-Rashba type)
and extrinsic (dynamical) spin-orbit coupling yields a nonlinear -
dependence of the spin Nernst and spin Hall conductivities.Comment: 9 pages, 4 figure
Spin Hall effects due to phonon skew scattering
A diversity of spin Hall effects in metallic systems is known to rely on Mott
skew scattering. In this work its high-temperature counterpart, phonon skew
scattering, which is expected to be of foremost experimental relevance, is
investigated. In particular, the phonon skew scattering spin Hall conductivity
is found to be practically -independent for temperatures above the Debye
temperature . As a consequence, in Rashba-like systems a high- linear
behavior of the spin Hall angle demonstrates the dominance of extrinsic
spin-orbit scattering only if the intrinsic spin splitting is smaller than the
temperature.Comment: Accepted version, 4 (+1) pages, 2 figure
Determination of the noise parameters in a one-dimensional open quantum system
We consider an electron magnetically interacting with a spin-1/2 impurity,
embedded in an external environment whose noisy term acts only on the
impurity's spin, and we find expressions for the electron transmission and
reflection probabilities in terms of the phenomenological noise parameters.
Moreover, we give a simple example of the necessity of complete positivity for
physical consistency, showing that a positive but not completely positive
dissipative map can lead to negative transmission probabilities
On the self-similar motion of a gravitating Chaplygin fluid
A self-similar motion of the generalized Chaplygin gas in its own
gravitational field is considered. The problem is being studied numerically and
analytically (in the limiting cases). It is shown that the model under
consideration admits only expanding solutions. As the astrophysical application
of the model, a description of rotating curves of spiral galaxies is suggested
by using the analytical solutions obtained in the paper.Comment: references are adde
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