13,632 research outputs found
Anomalous Spin Polarization of GaAs Two-Dimensional Hole Systems
We report measurements and calculations of the spin-subband depopulation,
induced by a parallel magnetic field, of dilute GaAs two-dimensional (2D) hole
systems. The results reveal that the shape of the confining potential
dramatically affects the values of in-plane magnetic field at which the upper
spin subband is depopulated. Most surprisingly, unlike 2D electron systems, the
carrier-carrier interaction in 2D hole systems does not significantly enhance
the spin susceptibility. We interpret our findings using a multipole expansion
of the spin density matrix, and suggest that the suppression of the enhancement
is related to the holes' band structure and effective spin j=3/2.Comment: 6 pages, 4 figures, substantially extended discussion of result
First results of observations of transient pulsar SAXJ2103.5+4545 with the INTEGRAL observatory
We present preliminary results of observations of X-ray pulsar SAX
J2103.5+4545 with INTEGRAL observatory in Dec 2002. Maps of this sky region in
energy bands 3-10, 15-40, 40-100 and 100-200 keV are presented. The source is
significantly detected up to energies of keV. The hard X-ray flux in
the 15-100 energy band is variable, that could be connected with the orbital
phase of the binary system. We roughly reconstructed the source spectrum using
its comparison to that of Crab nebula. It is shown that the parameters of the
source spectrum in 18-150 keV energy range are compatible with that obtained
earlier by RXTE observatoryComment: 5 pages, 4 figures, accepted for publication in the Astronomy Letter
Negative differential Rashba effect in two-dimensional hole systems
We demonstrate experimentally and theoretically that two-dimensional (2D)
heavy hole systems in single heterostructures exhibit a \emph{decrease} in
spin-orbit interaction-induced spin splitting with an increase in perpendicular
electric field. Using front and back gates, we measure the spin splitting as a
function of applied electric field while keeping the density constant. Our
results are in contrast to the more familiar case of 2D electrons where spin
splitting increases with electric field.Comment: 3 pages, 3 figures. To appear in AP
Spin-orbit interaction and asymmetry effects on Kondo ridges at finite magnetic field
We study electron transport through a serial double quantum dot with Rashba
spin-orbit interaction (SOI) and Zeeman field of amplitude B in presence of
local Coulomb repulsion. The linear conductance as a function of a gate voltage
Vg equally shifting the levels on both dots shows two B=0 Kondo ridges which
are robust against SOI as time-reversal symmetry is preserved. Resulting from
the crossing of a spin-up and a spin-down level at vanishing SOI two additional
Kondo plateaus appear at finite B. They are not protected by symmetry and
rapidly vanish if the SOI is turned on. Left-right asymmetric level-lead
couplings and detuned on-site energies lead to a simultaneous breaking of
left-right and bonding-anti-bonding state symmetry. In this case the finite-B
Kondo ridges in the Vg-B plane are bent with respect to the Vg-axis. For the
Kondo ridge to develop different level renormalizations must be compensated by
adjusting B.Comment: 8 pages, 5 figures, revised version as publishe
Theory of Spin Relaxation in Two-Electron Lateral Coupled Si/SiGe Quantum Dots
Highly accurate numerical results of phonon-induced two-electron spin
relaxation in silicon double quantum dots are presented. The relaxation,
enabled by spin-orbit coupling and the nuclei of Si (natural or purified
abundance), are investigated for experimentally relevant parameters, the
interdot coupling, the magnetic field magnitude and orientation, and the
detuning. We calculate relaxation rates for zero and finite temperatures (100
mK), concluding that our findings for zero temperature remain qualitatively
valid also for 100 mK. We confirm the same anisotropic switch of the axis of
prolonged spin lifetime with varying detuning as recently predicted in GaAs.
Conditions for possibly hyperfine-dominated relaxation are much more stringent
in Si than in GaAs. For experimentally relevant regimes, the spin-orbit
coupling, although weak, is the dominant contribution, yielding anisotropic
relaxation rates of at least two order of magnitude lower than in GaAs.Comment: 11 pages, 10 figure
INTEGRAL spectral variability study of the atoll 4U 1820-30: first detection of hard X-ray emission
We study the 4-200 keV spectral and temporal behaviour of the low mass X-ray
binary 4U 1820-30 with INTEGRAL during 2003-2005. This source as been observed
in both the soft (banana) and hard (island) spectral states. A high energy
tail, above 50 keV, in the hard state has been observed for the first time.
This places the source in the category of X-ray bursters showing high-energy
emission. The tail can be modeled as a soft power law component, with the
photon index of ~2.4, on top of thermal Comptonization emission from a plasma
with the electron temperature of kT_e~6 keV and optical depth of \tau~4.
Alternatively, but at a lower goodness of the fit, the hard-state broad band
spectrum can be accounted for by emission from a hybrid, thermal-nonthermal,
plasma. During this monitoring the source spent most of the time in the soft
state, usual for this source, and the >~4 keV spectra are represented by
thermal Comptonization with kT_e~3 keV and \tau~6-7.Comment: 14 pages, 4 figures, accepted for publication by Ap
Weak antilocalization in high mobility Ga(x)In(1-x)As/InP two-dimensional electron gases with strong spin-orbit coupling
We have studied the spin-orbit interaction in a high mobility two-dimensional
electron gas in a GaInAs/InP heterostructure as a function of an applied gate
voltage as well as a function of temperature. Highly sensitive magnetotransport
measurements of weak antilocalization as well as measurements of Shubnikov--de
Haas oscillations were performed in a wide range of electron sheet
concentrations. In our samples the electron transport takes place in the strong
spin precession regime in the whole range of applied gate voltages, which is
characterized by the spin precession length being shorter than the elastic mean
free path. The magnitude of the Rashba spin-orbit coupling parameter was
determined by fitting the experimental curves by a simulated quantum
conductance correction according to a model proposed recently by Golub [Phys.
Rev. B 71, 235310 (2005)]. A comparison of the Rashba coupling parameter
extracted using this model with the values estimated from the analysis of the
beating pattern in the Shubnikov--de Haas oscillations showed a good agreement.Comment: 5 pages, 5 figures, accepted for publication in Phys.Rev.
Coexistence in a One-Dimensional Cyclic Dominance Process
Cyclic (rock-paper-scissors-type) population models serve to mimic complex
species interactions. Focusing on a paradigmatic three-species model with
mutations in one dimension, we observe an interplay between equilibrium and
non-equilibrium processes in the stationary state. We exploit these insights to
obtain asymptotically exact descriptions of the emerging reactive steady state
in the regimes of high and low mutation rates. The results are compared to
stochastic lattice simulations. Our methods and findings are potentially
relevant for the spatio-temporal evolution of other non-equilibrium stochastic
processes.Comment: 4 pages, 4 figures and 2 pages of Supplementary Material. To appear
in Physical Review
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