1,290 research outputs found
Calculation of the Self-energy of Open Quantum Systems
We propose an easy method of calculating the self-energy of semi-infinite
leads attached to a mesoscopic system.Comment: 6 pages, 2 figures, published in J. Phys. Soc. Jp
Towards spin injection from silicon into topological insulators: Schottky barrier between Si and Bi2Se3
A scheme is proposed to electrically measure the spin-momentum coupling in
the topological insulator surface state by injection of spin polarized
electrons from silicon. As a first approach, devices were fabricated consisting
of thin (<100nm) exfoliated crystals of Bi2Se3 on n-type silicon with
independent electrical contacts to silicon and Bi2Se3. Analysis of the
temperature dependence of thermionic emission in reverse bias indicates a
barrier height of 0.34 eV at the Si-Bi2Se3 interface. This robust Schottky
barrier opens the possibility of novel device designs based on sub-band gap
internal photoemission from Bi2Se3 into Si
Tunneling ``zero-bias'' anomaly in the quasi-ballistic regime
For the first time, we study the tunneling density of states (DOS) of the
interacting electron gas beyond the diffusive limit. A strong correction to the
DOS persists even at electron energies exceeding the inverse transport
relaxation time, which could not be expected from the well-known
Altshuler-Aronov-Lee (AAL) theory. This correction originates from the
interference between the electron waves scattered by an impurity and by the
Friedel oscillation this impurity creates. Account for such processes also
revises the AAL formula for the DOS in the diffusive limit.Comment: 4 pages, 2 .eps figures, submitted to Phys. Rev. Let
Solar radiation on Mars: Stationary photovoltaic array
Solar energy is likely to be an important power source for surface-based operation on Mars. Photovoltaic cells offer many advantages. In this article we have presented analytical expressions and solar radiation data for stationary flat surfaces (horizontal and inclined) as a function of latitude, season and atmospheric dust load (optical depth). The diffuse component of the solar radiation on Mars can be significant, thus greatly affecting the optimal inclination angle of the photovoltaic surface
Coherent spin transport through a 350-micron-thick Silicon wafer
We use all-electrical methods to inject, transport, and detect spin-polarized
electrons vertically through a 350-micron-thick undoped single-crystal silicon
wafer. Spin precession measurements in a perpendicular magnetic field at
different accelerating electric fields reveal high spin coherence with at least
13pi precession angles. The magnetic-field spacing of precession extrema are
used to determine the injector-to-detector electron transit time. These transit
time values are associated with output magnetocurrent changes (from in-plane
spin-valve measurements), which are proportional to final spin polarization.
Fitting the results to a simple exponential spin-decay model yields a
conduction electron spin lifetime (T1) lower bound in silicon of over 500ns at
60K.Comment: Accepted in PR
Global properties of Stochastic Loewner evolution driven by Levy processes
Standard Schramm-Loewner evolution (SLE) is driven by a continuous Brownian
motion which then produces a trace, a continuous fractal curve connecting the
singular points of the motion. If jumps are added to the driving function, the
trace branches. In a recent publication [1] we introduced a generalized SLE
driven by a superposition of a Brownian motion and a fractal set of jumps
(technically a stable L\'evy process). We then discussed the small-scale
properties of the resulting L\'evy-SLE growth process. Here we discuss the same
model, but focus on the global scaling behavior which ensues as time goes to
infinity. This limiting behavior is independent of the Brownian forcing and
depends upon only a single parameter, , which defines the shape of the
stable L\'evy distribution. We learn about this behavior by studying a
Fokker-Planck equation which gives the probability distribution for endpoints
of the trace as a function of time. As in the short-time case previously
studied, we observe that the properties of this growth process change
qualitatively and singularly at . We show both analytically and
numerically that the growth continues indefinitely in the vertical direction
for , goes as for , and saturates for . The probability density has two different scales corresponding to
directions along and perpendicular to the boundary. In the former case, the
characteristic scale is . In the latter case the scale
is for , and
for . Scaling functions for the probability density are given for
various limiting cases.Comment: Published versio
Conduction through a quantum dot near a singlet-triplet transition
Kondo effect in the vicinity of a singlet-triplet transition in a vertical
quantum dot is considered. This system is shown to map onto a special version
of the two-impurity Kondo model. At any value of the control parameter, the
system has a Fermi-liquid ground state. Explicit expressions for the linear
conductance as a function of the control parameter and temperature are
obtained. At T=0, the conductance reaches the unitary limit at
the triplet side of the transition, and decreases with the increasing distance
to the transition at the singlet side. At finite temperature, the conductance
exhibits a peak near the transition point
Suppression of Kondo effect in a quantum dot by external irradiation
We demonstrate that the external irradiation brings decoherence in the spin
states of the quantum dot. This effect cuts off the Kondo anomaly in
conductance even at zero temperature. We evaluate the dependence of the DC
conductance in the Kondo regime on the power of irradiation, this dependence
being determined by the decoherence.Comment: 4 pages, 1 figur
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