38,510 research outputs found
Bias-controllable intrinsic spin polarization in a quantum dot
We propose a novel scheme to efficiently polarize and manipulate the electron
spin in a quantum dot. This scheme is based on the spin-orbit interaction and
it possesses following advantages: (1) The direction and the strength of the
spin polarization is well controllable and manipulatable by simply varying the
bias or the gate voltage. (2) The spin polarization is quite large even with a
weak spin-orbit interaction. (3) Both electron-electron interaction and
multi-energy levels do not weaken but strengthen the spin polarization. (4) It
has the short spin flip time. (5) The device is free of a magnetic field or a
ferromagnetic material. (6) It can be easily realized with present technology.Comment: 9 pages, 5 figure
Stark effect on the exciton spectra of vertically coupled quantum dots: horizontal field orientation and non-aligned dots
We study the effect of an electric-field on an electron-hole pair in an
asymmetric system of vertically coupled self-assembled quantum dots taking into
account their non-perfect alignment. We show that the non-perfect alignment
does not qualitatively influence the exciton Stark effect for the electric
field applied in the growth direction, but can be detected by application of a
perpendicular electric field. We demonstrate that the direction of the shift
between the axes of non-aligned dots can be detected by rotation of a weak
electric field within the plane of confinement. Already for a nearly perfect
alignment the two-lowest energy bright exciton states possess antilocked
extrema as function of the orientation angle of the horizontal field which
appear when the field is parallel to the direction of the shift between the dot
centers
Testing a new luminosity/redshift indicator for -ray bursts
We have tested a relative spectral lag (RSL) method suggested earlier as a
luminosity/redshift (or distance) estimator, using the generalized method by
Schaefer & Collazzi. We find the derivations from the luminosity/redshift-RSL
(L/R-RSL) relation are comparable with the corresponding observations. Applying
the luminosity-RSL relation to two different GRB samples, we find that there
exist no violators from the generalized test, namely the Nakar & Piran test and
Li test. We also find that about 36 per cent of Schaefer's sample are outliers
for the L/R-RSL relation within 1 confidence level, but no violators at
3 level within the current precision of L/R-RSL relation. An analysis
of several potential outliers for other luminosity relations shows they can
match the L/R-RSL relation well within an acceptable uncertainty. All the
coincident results seem to suggest that this relation could be a potential tool
for cosmological study.Comment: 7 pages, 6 figures and 1 table; Comments are welcom
Numerical simulations of a ballistic spin interferometer with the Rashba spin-orbital interaction
We numerically investigate the transport behavior of a quasi one-dimension
(1D) square loop device containing the Rashba spin-orbital interaction in the
presence of a magnetic flux. The conductance versus the magnetic field shows
the Al'tshuler-Aronov-Spivak (AAS) and Aharonov-Bohm (AB) oscillations. We
focus on the oscillatory amplitudes, and find that both of them are strongly
dependent on the spin precession angle (i.e. the strength of the spin-orbit
interaction) and exhibit no-periodic oscillations, which are well in agreement
with a recent experiment by Koga et al. [cond-mat/0504743(unpublished)].
However, our numerical results for the ideal 1D square loop device for the node
positions of the amplitudes of the AB and AAS oscillations are found to be of
some discrepancies comparing with quasi-1D square loop with a finite width. In
the presence of disorder and taking the disorder ensemble average, the AB
oscillation in the conductance will disappear, while the time-reversal
symmetric AAS oscillation still remains. Furthermore, the node positions of the
AAS oscillatory amplitude remains the same.Comment: 6 pages, 7 figure
Pre-selectable integer quantum conductance of electrochemically fabricated silver point contacts
The controlled fabrication of well-ordered atomic-scale metallic contacts is
of great interest: it is expected that the experimentally observed high
percentage of point contacts with a conductance at non-integer multiples of the
conductance quantum G_0 = 2e^2/h in simple metals is correlated to defects
resulting from the fabrication process. Here we demonstrate a combined
electrochemical deposition and annealing method which allows the controlled
fabrication of point contacts with pre-selectable integer quantum conductance.
The resulting conductance measurements on silver point contacts are compared
with tight-binding-like conductance calculations of modeled idealized junction
geometries between two silver crystals with a predefined number of contact
atoms
A multitemporal remote sensing approach to parsimonious streamflow modeling in a southcentral Texas watershed, USA
International audienceSoil moisture condition plays a vital role in a watershed's hydrologic response to a precipitation event and is thus parameterized in most, if not all, rainfall-runoff models. Yet the soil moisture condition antecedent to an event has proven difficult to quantify both spatially and temporally. This study assesses the potential to parameterize a parsimonious streamflow prediction model solely utilizing precipitation records and multi-temporal remotely sensed biophysical variables (i.e.~from Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra satellite). This study is conducted on a 1420 km2 rural watershed in the Guadalupe River basin of southcentral Texas, a basin prone to catastrophic flooding from convective precipitation events. A multiple regression model, accounting for 78% of the variance of observed streamflow for calendar year 2004, was developed based on gauged precipitation, land surface temperature, and enhanced vegetation Index (EVI), on an 8-day interval. These results compared favorably with streamflow estimations utilizing the Natural Resources Conservation Service (NRCS) curve number method and the 5-day antecedent moisture model. This approach has great potential for developing near real-time predictive models for flood forecasting and can be used as a tool for flood management in any region for which similar remotely sensed data are available
Power Law Distribution of Wealth in a Money-Based Model
A money-based model for the power law distribution (PLD) of wealth in an
economically interacting population is introduced. The basic feature of our
model is concentrating on the capital movements and avoiding the complexity of
micro behaviors of individuals. It is proposed as an extension of the Equiluz
and Zimmermann's (EZ) model for crowding and information transmission in
financial markets. Still, we must emphasize that in EZ model the PLD without
exponential correction is obtained only for a particular parameter, while our
pattern will give it within a wide range. The Zipf exponent depends on the
parameters in a nontrivial way and is exactly calculated in this paper.Comment: 5 pages and 4 figure
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