22,860 research outputs found
Mesoscopic Spin Hall Effect
We investigate the spin Hall effect in ballistic chaotic quantum dots with
spin-orbit coupling. We show that a longitudinal charge current can generate a
pure transverse spin current. While this transverse spin current is generically
nonzero for a fixed sample, we show that when the spin-orbit coupling time is
large compared to the mean dwell time inside the dot, it fluctuates universally
from sample to sample or upon variation of the chemical potential with a
vanishing average. For a fixed sample configuration, the transverse spin
current has a finite typical value ~e^2 V/h, proportional to the longitudinal
bias V on the sample, and corresponding to about one excess open channel for
one of the two spin species. Our analytical results are in agreement with
numerical results in a diffusive system [W. Ren et al., Phys. Rev. Lett. 97,
066603 (2006)] and are further confirmed by numerical simulation in a chaotic
cavity.Comment: 4 pages, 2 figure
Multilayers of Zinc-Blende Half-Metals with Semiconductors
We report on first-principles calculations of multilayers of zinc-blende
half-metallic ferromagnets CrAs and CrSb with III-V and II-VI semiconductors,
in the [001] orientation. We examine the ideal and tetragonalised structures,
as well as the case of an intermixed interface. We find that, as a rule,
half-metallicity can be conserved throughout the heterostructures, provided
that the character of the local coordination and bonding is not disturbed. At
the interfaces with semiconductors, we describe a mechanism that can give also
a non-integer spin moment per interface transition atom, and derive a simple
rule to evaluate it
High accuracy results for the energy levels of the molecular ions H2+, D2+ and HD+, up to J=2
We present a nonrelativistic calculation of the rotation-vibration levels of
the molecular ions H2+, D2+ and HD+, relying on the diagonalization of the
exact three-body Hamiltonian. The J=2 levels are obtained with a very high
accuracy of 10^{-14} a.u. (for most levels) representing an improvement by five
orders of magnitude over previous calculations. The accuracy is also improved
for the J=1 levels of H2+ and D2+ with respect to earlier works. Moreover, we
have computed the sensitivities of the energy levels with respect to the mass
ratios, allowing these levels to be used for metrological purposes.Comment: 11 page
Current Issues in Remote Sensing
In this article certain problems surrounding Satellite remote sensing (SRS) will be addressed with particular emphasis on their legal implications. Aspects of air law as they affect remote sensing will not be discussed in any detail, nor will it be necessary to refer to the vexing problem of determining the satisfactory boundary between the airspace and outer space. This fundamental problem is still in dispute and under constant review, both in scholarly circles and in the United Nations; and the world community may consider itself fortunate that the issue has not prevented a number of important international agreements on space law from being adopted. The status of SRS in the regimes created by these agreements will be the focus of this article
Experimental Test of Relativistic Quantum State Collapse with Moving Reference Frames
An experimental test of relativistic wave-packet collapse is presented. The
tested model assumes that the collapse takes place in the reference frame
determined by the massive measuring detectors. Entangled photons are measured
at 10 km distance within a time interval of less than 5 ps. The two apparatuses
are in relative motion so that both detectors, each in its own inertial
reference frame, are first to perform the measurement. The data always
reproduces the quantum correlations and thus rule out a class of collapse
models. The results also set a lower bound on the "speed of quantum
information" to 0.66 x 10^7 and 1.5 x 10^4 times the speed of light in the
Geneva and the background radiation reference frames, respectively. The very
difficult and deep question of where the collapse takes place - if it takes
place at all - is considered in a concrete experimental context.Comment: 4 pages + 2 ps figure
Scattering Theory of Current-Induced Spin Polarization
We construct a novel scattering theory to investigate magnetoelectrically
induced spin polarizations. Local spin polarizations generated by electric
currents passing through a spin-orbit coupled mesoscopic system are measured by
an external probe. The electrochemical and spin-dependent chemical potentials
on the probe are controllable and tuned to values ensuring that neither charge
nor spin current flow between the system and the probe, on time-average. For
the relevant case of a single-channel probe, we find that the resulting
potentials are exactly independent of the transparency of the contact between
the probe and the system. Assuming that spin relaxation processes are absent in
the probe, we therefore identify the local spin-dependent potentials in the
sample at the probe position, and hence the local current-induced spin
polarization, with the spin-dependent potentials in the probe itself. The
statistics of these local chemical potentials is calculated within random
matrix theory. While they vanish on spatial and mesoscopic average, they
exhibit large fluctuations, and we show that single systems typically have spin
polarizations exceeding all known current-induced spin polarizations by a
parametrically large factor. Our theory allows to calculate quantum
correlations between spin polarizations inside the sample and spin currents
flowing out of it. We show that these large polarizations correlate only weakly
with spin currents in external leads, and that only a fraction of them can be
converted into a spin current in the linear regime of transport, which is
consistent with the mesoscopic universality of spin conductance fluctuations.
We numerically confirm the theory.Comment: Final version; a tunnel barrier between the probe and the dot is
considered. To appear in 'Nanotechnology' in the special issue on "Quantum
Science and Technology at the Nanoscale
Identification of new transitional disk candidates in Lupus with Herschel
New data from the Herschel Space Observatory are broadening our understanding
of the physics and evolution of the outer regions of protoplanetary disks in
star forming regions. In particular they prove to be useful to identify
transitional disk candidates. The goals of this work are to complement the
detections of disks and the identification of transitional disk candidates in
the Lupus clouds with data from the Herschel Gould Belt Survey. We extracted
photometry at 70, 100, 160, 250, 350 and 500 m of all spectroscopically
confirmed Class II members previously identified in the Lupus regions and
analyzed their updated spectral energy distributions. We have detected 34 young
disks in Lupus in at least one Herschel band, from an initial sample of 123
known members in the observed fields. Using the criteria defined in Ribas et
al. (2013) we have identified five transitional disk candidates in the region.
Three of them are new to the literature. Their PACS-70 m fluxes are
systematically higher than those of normal T Tauri stars in the same
associations, as already found in T Cha and in the transitional disks in the
Chamaeleon molecular cloud. Herschel efficiently complements mid-infrared
surveys for identifying transitional disk candidates and confirms that these
objects seem to have substantially different outer disks than the T Tauri stars
in the same molecular clouds.Comment: Accepted for publication in A&A. 16 pages, 9 figures, 7 table
Efficiency at maximum power of thermally coupled heat engines
We study the efficiency at maximum power of two coupled heat engines, using
thermoelectric generators (TEGs) as engines. Assuming that the heat and
electric charge fluxes in the TEGs are strongly coupled, we simulate
numerically the dependence of the behavior of the global system on the
electrical load resistance of each generator in order to obtain the working
condition that permits maximization of the output power. It turns out that this
condition is not unique. We derive a simple analytic expression giving the
relation between the electrical load resistance of each generator permitting
output power maximization. We then focuse on the efficiency at maximum power
(EMP) of the whole system to demonstrate that the Curzon-Ahlborn efficiency may
not always be recovered: the EMP varies with the specific working conditions of
each generator but remains in the range predicted by irreversible
thermodynamics theory. We finally discuss our results in light of non-ideal
Carnot engine behavior.Comment: 11 pages, 7 figure
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