5,999 research outputs found
Diffuse emission in the presence of inhomogeneous spin-orbit interaction for the purpose of spin filtration
A lateral interface connecting two regions with different strengths of the
Bychkov-Rashba spin-orbit interaction can be used as a spin polarizer of
electrons in two dimensional semiconductor heterostructures. [Khodas \emph{et
al.}, Phys. Rev. Lett. \textbf{92}, 086602 (2004)]. In this paper we consider
the case when one of the two regions is ballistic, while the other one is
diffusive. We generalize the technique developed for the solution of the
problem of the diffuse emission to the case of the spin dependent scattering at
the interface, and determine the distribution of electrons emitted from the
diffusive region. It is shown that the diffuse emission is an effective way to
get electrons propagating at small angles to the interface that are most
appropriate for the spin filtration and a subsequent spin manipulation.
Finally, a scheme is proposed of a spin filter device, see Fig. 9, that creates
two almost fully spin-polarized beams of electrons.Comment: 11 pages, 9 figure
Orbital magnetoelectric coupling in band insulators
Magnetoelectric responses are a fundamental characteristic of materials that
break time-reversal and inversion symmetries (notably multiferroics) and,
remarkably, of "topological insulators" in which those symmetries are unbroken.
Previous work has shown how to compute spin and lattice contributions to the
magnetoelectric tensor. Here we solve the problem of orbital contributions by
computing the frozen-lattice electronic polarization induced by a magnetic
field. One part of this response (the "Chern-Simons term") can appear even in
time-reversal-symmetric materials and has been previously shown to be quantized
in topological insulators. In general materials there are additional orbital
contributions to all parts of the magnetoelectric tensor; these vanish in
topological insulators by symmetry and also vanish in several simplified models
without time-reversal and inversion those magnetoelectric couplings were
studied before. We give two derivations of the response formula, one based on a
uniform magnetic field and one based on extrapolation of a long-wavelength
magnetic field, and discuss some of the consequences of this formula.Comment: 13 page
High field transport in strained Si/GeSi double heterostructure: a Fokker-Planck approach
We report calculations of high electric field transport for the case of a
strained Si/GeSi double heterostructure (DHS) considering transport along the
Si channel and by applying the analytical Fokker-Planck approach (FPA), where
the process is modeled as drift-diffusion in energy space. We limit ourselves
to electronic transport in the conduction band of the strained Si, where an
energy shift between the otherwise degenerate six energy valleys characterizes
the band alingment in the DHS. Intervalley phonon scatterings are considered
while intravalley acoustic phonon scattering is ignored, leading to results
valid for high enough temperatures. Our results are compared to previous
theoretical works where Monte Carlo simulations were applied. A reasonable
agreement between the two approaches is obtained in the high electric field
regime.Comment: 8 pages, 3 figure
Giant isotope effect in the incoherent tunneling specific heat of the molecular nanomagnet Fe8
Time-dependent specific heat experiments on the molecular nanomagnet Fe8 and
the isotopic enriched analogue 57Fe8 are presented. The inclusion of the 57Fe
nuclear spins leads to a huge enhancement of the specific heat below 1 K,
ascribed to a strong increase in the spin-lattice relaxation rate Gamma arising
from incoherent, nuclear-spin-mediated magnetic quantum tunneling in the
ground-doublet. Since Gamma is found comparable to the expected tunneling rate,
the latter process has to be inelastic. A model for the coupling of the
tunneling levels to the lattice is presented. Under transverse field, a
crossover from nuclear-spin-mediated to phonon-induced tunneling is observed.Comment: Replaced with version accepted for publication in Physical Review
Letter
Nonlinear I-V Characteristics of a Mesoscopic Conductor
We present a general theoretical formulation, based on nonequilibrium Green's
functions, for nonlinear DC transport in multi-probe mesoscopic conductors. The
theory is gauge invariant and is useful for the predictions of current-voltage
characteristics and the nonequilibrium charge pile-ups inside the conductor. We
have provided a detailed comparison between the gauge invariant scattering
matrix theory and our theory. We have also given several examples where the I-V
curve can be obtained analytically. The effects of exchange and correlation
have been considered explicitly
Quantum dot dephasing by edge states
We calculate the dephasing rate of an electron state in a pinched quantum
dot, due to Coulomb interactions between the electron in the dot and electrons
in a nearby voltage biased ballistic nanostructure. The dephasing is caused by
nonequilibrium time fluctuations of the electron density in the nanostructure,
which create random electric fields in the dot. As a result, the electron level
in the dot fluctuates in time, and the coherent part of the resonant
transmission through the dot is suppressed
Acoustoelectric current and pumping in a ballistic quantum point contact
The acoustoelectric current induced by a surface acoustic wave (SAW) in a
ballistic quantum point contact is considered using a quantum approach. We find
that the current is of the "pumping" type and is not related to drag, i.e. to
the momentum transfer from the wave to the electron gas. At gate voltages
corresponding to the plateaus of the quantized conductance the current is
small. It is peaked at the conductance step voltages. The peak current
oscillates and decays with increasing SAW wavenumber for short wavelengths.
These results contradict previous calculations, based on the classical
Boltzmann equation.Comment: 4 pages, 1 figur
Calorimetry of gamma-ray bursts: echos in gravitational waves
Black holes surrounded by a disk or torus may drive the enigmatic
cosmological gamma-ray bursts (GRBs). Equivalence in poloidal topology to
pulsar magnetospheres shows a high incidence of the black hole-luminosity
into the surrounding magnetized matter. We argue that this emission is
re-radiated into gravitational waves at in frequencies of
order 1kHz, winds and, potentially, MeV neutrinos. The total energy budget and
input to the GRB from baryon poor jets are expected to be standard in this
scenario, consistent with recent analysis of afterglow data. Collimation of
these outflows by baryon rich disk or torus winds may account for the observed
spread in opening angles up to about . This model may be tested by future
LIGO/VIRGO observations.Comment: To appear in ApJ
Landauer Conductance of Luttinger Liquids with Leads
We show that the dc conductance of a quantum wire containing a Luttinger
liquid and attached to non-interacting leads is given by per spin
orientation, regardless of the interactions in the wire. This explains the
recent observations of the absence of conductance renormalization in long
high-mobility wires by Tarucha, Honda and Saku (Solid State
Communications {\bf 94}, 413 (1995)).Comment: 4 two-column pages, RevTeX + 1 uuencoded figure
Classical properties of low-dimensional conductors: Giant capacitance and non-Ohmic potential drop
Electrical field arising around an inhomogeneous conductor when an electrical
current passes through it is not screened, as distinct from 3D conductors, in
low-dimensional conductors. As a result, the electrical field depends on the
global distribution of the conductivity sigma(x) rather than on the local value
of it, inhomogeneities of sigma(x) produce giant capacitances C(omega) that
show frequency dependence at relatively low omega, and electrical fields
develop in vast regions around the inhomogeneities of sigma(x). A theory of
these phenomena is presented for 2D conductors.Comment: 5 pages, two-column REVTeX, to be published in Physical Review
Letter
- …