3,724 research outputs found
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
- β¦