1,135 research outputs found
Analytical result on the supercurrent through a superconductor/quantum-dot/superconductor junction
We present an analytical result for the supercurrent across a
superconductor/quantum-dot/superconductor junction. By converting the current
integration into a special contour integral, we can express the current as a
sum of the residues of poles. These poles are real and give a natural
definition of the Andreev bound states. We also use the exact result to explain
some features of the supercurrent transport behavior.Comment: 8 pages, 2 figure
Andreev reflection through a quantum dot coupled with two ferromagnets and a superconductor
We study the Andreev reflection (AR) in a three terminal mesoscopic hybrid
system, in which two ferromagnets (F and F) are coupled to a
superconductor (S) through a quantum dot (QD). By using non-equilibrium Green
function, we derive a general current formula which allows arbitrary spin
polarizations, magnetization orientations and bias voltages in F and F.
The formula is applied to study both zero bias conductance and finite bias
current. The current conducted by crossed AR involving F, F and S is
particularly unusual, in which an electron with spin incident from
one of the ferromagnets picks up another electron with spin from
the other one, both enter S and form a Cooper pair. Several special cases are
investigated to reveal the properties of AR in this system.Comment: 15 pages, 7 figures, LaTe
Probing Spin States of Coupled Quantum Dots by dc Josephson Current
We propose an idea for probing spin states of two coupled quantum dots (CQD),
by the dc Josephson current flowing through them. This theory requires weak
coupling between CQD and electrodes, but allows arbitrary inter-dot tunnel
coupling, intra- and inter- dot Coulomb interactions. We find that the Coulomb
blockade peaks exhibit a non-monotonous dependence on the Zeeman splitting of
CQD, which can be understood in terms of the Andreev bound states. More
importantly, the supercurrent in the Coulomb blockade valleys may provide the
information of the spin states of CQD: for CQD with total electron number N=1,3
(odd), the supercurrent will reverse its sign if CQD becomes a magnetic
molecule; for CQD with N=2 (even), the supercurrent will decrease sharply
around the transition between the spin singlet and triplet ground states of
CQD.Comment: 10 pages, 3 figure
Theory of Nonequilibrium Coherent Transport through an Interacting Mesoscopic Region Weakly Coupled to Electrodes
We develop a theory for the nonequilibrium coherent transport through a
mesoscopic region, based on the nonequilibrium Green function technique. The
theory requires the weak coupling between the central mesoscopic region and the
multiple electrodes connected to it, but allows arbitrary hopping and
interaction in the central region. An equation determining the nonequilibrium
distribution in the central interacting region is derived and plays an
important role in the theory. The theory is applied to two special cases for
demonstrations, revealing the novel effects associated with the combination of
phase coherence, Coulomb interaction, and nonequilibrium distribution.Comment: 10 Pages, 5 figure
Photon-assisted Fano Resonance and Corresponding Shot-Noise in a Quantum Dot
We have studied the Fano resonance in photon-assisted transport in a quantum
dot and calculated both the coherent current and spectral density of shot
noise. It is predicted, for the first time, that the shape of Fano profile will
also appear in satellite peaks. It is found that the variations of Fano
profiles with the strengths of nonresonant transmissions are not synchronous in
absorption and emission sidebands. The effect of interference on
photon-assisted pumped current has been also investigated. We further predict
the current and spectral density of shot noise as a function of the phase,
which exhibits an intrinsic property of resonant and nonresonant channels in
the structures.Comment: 4 pages, 5 figure
SPATIAL-SPECTRAL UNMIXING OF HYPERSPECTRAL DATA FOR DETECTION AND ANALYSIS OF ASTROPHYSICAL SOURCES WITH THE MUSE INSTRUMENT
International audienceDetection and analysis of astrophysical sources from the forthcoming MUSE instrument is of greatest challenge mainly due to the high noise level and the three-dimensional translation variant blur effect of MUSE data. In this work, we use some realistic hypotheses of MUSE to reformulate the data convolution model into a set of linear mixing models corresponding to different, disjoint spectral frames. Based on the linear mixing models, we propose a spatial-spectral unmixing (SSU) algorithm to detect and characterize the galaxy spectra. In each spectral frame, the SSU algorithm identifies the pure galaxy regions with a theoretical guarantee, and estimate spectra based on a sparse approximation assumption. The full galaxy spectra can finally be recovered by concatenating the spectra estimates associated with all the spectral frames. The simulations were performed to demonstrate the efficacy of the proposed SSU algorithm
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