480 research outputs found
Intrinsic spin dynamics in semiconductor quantum dots
We investigate the characteristic spin dynamics corresponding to
semiconductor quantum dots within the multiband envelope function approximation
(EFA). By numerically solving an Hamiltonian we treat
systems based on different III-V semiconductor materials.It is shown that, even
in the absence of an applied magnetic field, these systems show intrinsic spin
dynamics governed by intraband and interband transitions leading to
characteristic spin frequencies ranging from the THz to optical frequencies.Comment: to be published in Nanotechnology. Separated figure file
Persistent spin and charge currents and magnification effects in open ring conductors subject to Rashba coupling
We analyze the effect of Rashba spin-orbit coupling and of a local tunnel
barrier on the persistent spin and charge currents in a one-dimensional
conducting Aharonov-Bohm (AB) ring symmetrically coupled to two leads. First,
as an important consequence of the spin-splitting, it is found that a
persistent spin current can be induced which is not simply proportional to the
charge current. Second, a magnification effect of the persistent spin current
is shown when one tunes the Fermi energy near the Fano-type antiresonances of
the total transmission coefficient governed by the tunnel barrier strength. As
an unambiguous signature of spin-orbit coupling we also show the possibility to
produce a persistent pure spin current at the interference zeros of the
transmittance. This widens the possibilities of employing mesoscopic conducting
rings in phase-coherent spintronics applications.Comment: 6 pages, 5 figures, to appear in PR
Charge transport in two dimensional electron gas/superconductor junctions with Rashba spin-orbit coupling
We have studied the tunneling conductance in two dimensional electron gas /
insulator / superconductor junctions in the presence of Rashba spin-orbit
coupling (RSOC). It is found that for low insulating barrier the tunneling
conductance is suppressed by the RSOC while for high insulating barrier it is
almost independent of the RSOC. We also find the reentrant behavior of the
conductance at zero voltage as a function of RSOC for intermediate insulating
barrier strength. The results are essentially different from those predicted in
ferromagnet / superconductor junctions. The present derivation of the
conductance is applicable to arbitrary velocity operator with off-diagonal
components.Comment: 8 pages, 6 figure
Spin Transport in Disordered Two-Dimensional Hopping Systems with Rashba Spin-Orbit Interaction
The influence of Rashba spin-orbit interaction on the spin dynamics of a
topologically disordered hopping system is studied in this paper. This is a
significant generalization of a previous investigation, where an ordered
(polaronic) hopping system has been considered instead. It is found, that in
the limit, where the Rashba length is large compared to the typical hopping
length, the spin dynamics of a disordered system can still be described by the
expressions derived for an ordered system, under the provision that one takes
into account the frequency dependence of the diffusion constant and the
mobility (which are determined by charge transport and are independent of
spin). With these results we are able to make explicit the influence of
disorder on spin related quantities as, e.g., the spin life-time in hopping
systems.Comment: 12 pages, 6 figures, some clarifications adde
Electron locking in semiconductor superlattices
We describe a novel state of electrons and phonons arising in semiconductor
superlattices (SSL) due to strong electron-phonon interactions. These states
are characterized by a localization of phonons and a self-trapping or locking
of electrons in one or several quantum wells due to an additional,
deformational potential arising around these locking wells in SSL. The effect
is enhanced in a longitudinal magnetic field.
Using the tight-binding and adiabatic approximations the whole energy
spectrum of the self-trapped states is found and accurate, analytic expressions
are included for strong electron-phonon coupling. Finally, we discuss possible
experiments which may detect these predicted self-trapped states.Comment: 8 pages, 2 figures. Please note that the published article has the
title 'Electron locking in layered structures by a longitudinal magnetic
field
Two Anderson impurities in a 2D host with Rashba spin-orbit interaction
We have studied the two-dimensional two-impurity Anderson model with
additional Rashba spin-orbit interaction by means of the modified perturbation
theory. The impurity Green's functions we have constructed exactly reproduce
the first four spectral moments. We discuss the height and the width of the
even/odd Kondo peaks as functions of the inter-impurity distance and the Rashba
energy (the strength of the Rashba spin-orbit interaction). For small
impurity separations the Kondo temperature shows a non-monotonic dependence on
being different in the even and the odd channel. We predict that the
Kondo temperature has only almost linear dependence on and not an
exponential increase with Comment: To be published in Phys. Rev.
Nuclear Dynamics During Landau-Zener Singlet-Triplet Transitions in Double Quantum Dots
We consider nuclear spin dynamics in a two-electron double dot system near
the intersection of the electron spin singlet and the lower energy
component of the spin triplet. The electron spin interacts with nuclear
spins and is influenced by the spin-orbit coupling. Our approach is based on a
quantum description of the electron spin in combination with the coherent
semiclassical dynamics of nuclear spins. We consider single and double
Landau-Zener passages across the - anticrossings. For linear sweeps,
the electron dynamics is expressed in terms of parabolic cylinder functions.
The dynamical nuclear polarization is described by two complex conjugate
functions related to the integrals of the products of the
singlet and triplet amplitudes
along the sweep. The real part of is related to the
- spin-transition probability, accumulates in the vicinity of the
anticrossing, and for long linear passages coincides with the Landau-Zener
probability , where is the Landau-Zener
parameter. The imaginary part of is specific for the nuclear
spin dynamics, accumulates during the whole sweep, and for
is typically an order of magnitude larger than . has a profound effect
on the nuclear spin dynamics, by (i) causing intensive shake-up processes among
the nuclear spins and (ii) producing a high nuclear spin generation rate when
the hyperfine and spin-orbit interactions are comparable in magnitude. We find
analytical expressions for the back-action of the nuclear reservoir represented
via the change in the Overhauser fields the electron subsystem experiences.Comment: 19 pages, 5 figure
Improved limit on electron neutrino charge radius through a new evaluation of the weak mixing angle
We have obtained a new limit on the electron neutrino effective charge radius
from a new evaluation of the weak mixing angle by a combined fit of all
electron-(anti)neutrino electron elastic scattering measurements. Weak mixing
angle is found to be sin^2 theta_W=0.259 \pm 0.025 in the low energy regime
below 100 MeV. The electron neutrino charge radius squared is bounded to be in
the range -0.13 10^-32 cm^2 < r^2 < 3.32 10^-32 cm^2 at 90 % C.L. Both results
improve previously published analyses. We also discuss perspectives of future
experiments to improve these constraints.Comment: 10 pages, 2 figures. Final published versio
Spontaneous generation of spin-orbit coupling in magnetic dipolar Fermi gases
The stability of an unpolarized two-component dipolar Fermi gas is studied
within mean-field theory. Besides the known instability towards spontaneous
magnetization with Fermi sphere deformation, another instability towards
spontaneous formation of a spin-orbit coupled phase with a Rashba-like spin
texture is found. A phase diagram is presented and consequences are briefly
discussed
Spontaneous spin-polarized current in a nonuniform Rashba interaction system
We investigate the electron transport through a two-dimensional semiconductor
with a nonuniform Rashba spin-orbit interaction. Due to the combination of the
coherence effect and the Rashba interaction, a spontaneous spin-polarized
current emerges in the absence of any magnetic material and magnetic field. For
a two-terminal device, only the local current contains polarization; however,
with a four-terminal setup, a polarized total current is produced. This
phenomenon may offer a novel way for generating a spin-polarized current,
replacing the traditional spin-injection method.Comment: 4 pages, 4 figure
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