309,679 research outputs found
Cooper Instability in the Occupation Dependent Hopping Hamiltonians
A generic Hamiltonian, which incorporates the effect of the orbital
contraction on the hopping amplitude between the nearest sites, is studied both
analytically at the weak coupling limit and numerically at the intermediate and
strong coupling regimes for finite atomic cluster. The effect of the orbital
contraction due to hole localization at atomic sites is specified with two
coupling parameters V and W (multiplicative and additive contraction terms).
The singularity of the vertex part of the two-particle Green's function
determines the critical temperature Tc and the relaxation rate Gamma(T) of the
order parameter at temperature above Tc. Unlike in conventional BCS
superconductors, Gamma has a non-zero imaginary part which may influence the
fluctuation conductivity of superconductor above Tc. We compute the ground
state energy as a function of the particle number and magnetic flux through the
cluster, and show the existence of the parity gap Delta appearing at the range
of system parameters consistent with the appearance of Cooper instability.
Numeric calculation of the Hubbard model (with U>0) at arbitrary occupation
does not show any sign of superconductivity in small cluster.Comment: 13 pages, 12 figure
Jordanian Solutions of Simplex Equations
We construct for all a solution of the Frenkel--Moore --simplex
equation which generalizes the --matrix for the Jordanian quantum group.Comment: 6 page
Pneumatic power is transmitted through air bearing
A more efficient method for supplying high pressure air to an air bearing and pneumatic equipment mounted on it has been developed. The system uses a conventional air bearing and an air-supported sphere with a central passage. High pressure air is channeled through it into the pneumatic equipment on the sphere
Non-adiabatic Josephson Dynamics in Junctions with in-Gap Quasiparticles
Conventional models of Josephson junction dynamics rely on the absence of low
energy quasiparticle states due to a large superconducting gap. With this
assumption the quasiparticle degrees of freedom become "frozen out" and the
phase difference becomes the only free variable, acting as a fictitious
particle in a local in time Josephson potential related to the adiabatic and
non-dissipative supercurrent across the junction. In this article we develop a
general framework to incorporate the effects of low energy quasiparticles
interacting non-adiabatically with the phase degree of freedom. Such
quasiparticle states exist generically in constriction type junctions with high
transparency channels or resonant states, as well as in junctions of
unconventional superconductors. Furthermore, recent experiments have revealed
the existence of spurious low energy in-gap states in tunnel junctions of
conventional superconductors - a system for which the adiabatic assumption
typically is assumed to hold. We show that the resonant interaction with such
low energy states rather than the Josephson potential defines nonlinear
Josephson dynamics at small amplitudes.Comment: 9 pages, 1 figur
- …