39 research outputs found
Nonequilibrium Cooper pairing in the nonadiabatic regime
We obtain a complete solution for the mean-field dynamics of the BCS paired
state with a large, but finite number of Cooper pairs in the non-adiabatic
regime. We show that the problem reduces to a classical integrable Hamiltonian
system and derive a complete set of its integrals of motion. The condensate
exhibits irregular multi-frequency oscillations ergodically exploring the part
of the phase-space allowed by the conservation laws. In the thermodynamic limit
however the system can asymptotically reach a steady state.Comment: 4 pages, no figure
Vortex mediated microwave absorption in superclean layered superconductors
In the superclean case the spectrum of vortex core excitations in the
presence of disorder is not random but consists of two series of equally-spaced
levels. The I-V characteristics of such superconductors displays many
interesting phenomena. A series of resonances is predicted at frequencies
commensurate with the spacing of the vortex excitations. These resonances
reveal an even-odd anomaly. In the presence of one weak impurity the excitation
levels can approach each other and almost cross. Absorption at very low
frequencies is identified with the resonances arising in this case. The results
of such microscopic theory coincide up to the order of magnitude with both the
theory employing kinetic equation and the experiment. The non-linear effects
associated with Zener transitions in such crossings are studied. These
phenomena can be used as a probe of vortex core excitations.Comment: 11 pages, 2 Postscript figure
Bi-stability in voltage-biased NISIN structures
As a generic example of a voltage-driven superconducting structure we study a
short superconductor connected to normal leads by means of low transparency
tunnel junctions, with a voltage bias between the leads. The
superconducting order parameter is to be determined self-consistently.
We study the stationary states of the system as well as the dynamics after a
perturbation. We find a region in parameter space where there are two stable
stationary states at a given voltage. These bi-stable states are distinguished
by distinct values of the superconducting order parameter and of the
current between the leads. We have evaluated (1) the multi-valued
superconducting order parameter at given ; (2) the current between
the leads at a given V; and (3) the critical voltage at which superconductivity
in the island ceases. With regards to dynamics, we find numerical evidence that
the stationary states are stable and that no complicated non-stationary regime
can be induced by changing the voltage. This result is somewhat unexpected and
by no means trivial, given the fact that the system is driven out of
equilibrium. The response to a change in the voltage is always gradual, even in
the regime where changing the interaction strength induces rapid anharmonic
oscillations of the order parameter.Comment: 15 pages, 11 figures, submitted to Phys. Rev.