1,288 research outputs found
Delocalization in two dimensional disordered Bose systems and depinning transition in the vortex state in superconductors
We investigate two-dimensional Bose system with the long range interactions
in the presence of disorder. Formation of the bound states at strong impurity
sites gives rise to an additional depletion of the superfluid density. We
demonstrate the existence of the intermediate superfluid state where the
condensate and localized bosons present simultaneously. We find that
interactions suppress localization and that with the increase of the boson
density the system experiences a sharp delocalization crossover into a state
where all bosons are delocalized. We map our results onto the three dimensional
system of vortices in type II superconductors in the presence of columnar
defects; the intermediate superfluid state maps to an intermediate vortex
liquid where vortex liquid neighbors pinned vortices. We predict the depinning
transition within the vortex liquid and depinning induced vortex lattice/Bose
glass melting
Quantum tunneling between paramagnetic and superconducting states of a nanometer-scale superconducting grain placed in a magnetic field
We consider the process of quantum tunneling between the superconducting and
paramagnetic states of a nanometer-scale superconducting grain placed in a
magnetic field. The grain is supposed to be coupled via tunneling junction to a
normal metallic contact that plays a role of the spin reservoir. Using the
instanton method we find the probability of the quantum tunneling process and
express it in terms of the applied magnetic field, order parameter of the
superconducting grain and conductance of the tunneling junction between the
grain and metallic contact
Barriers in the p-spin interacting spin-glass model. The dynamical approach
We investigate the barriers separating metastable states in the spherical
p-spin glass model using the instanton method. We show that the problem of
finding the barrier heights can be reduced to the causal two-real-replica
dynamics. We find the probability for the system to escape one of the highest
energy metastable states and the energy barrier corresponding to this process.Comment: 4 pages, 1 figur
Josephson transport through a Hubbard impurity center
We investigate the Josephson transport through a thin semiconductor barrier
containing impurity centers with the on-site Hubbard interaction of an
arbitrary sign and strength. We find that in the case of the repulsive
interaction the Josephson current changes sign with the temperature increase if
the energy of the impurity level (measured from the Fermi energy of
superconductors) falls in the interval . We predict strong temporal
fluctuations of the current if only a few centers present within the junction.
In the case of the attractive impurity potential () and at low
temperatures, the model is reduced to the effective two level Hamiltonian
allowing thus a simple description of the nonstationary Josephson effect in
terms of pair tunneling processes
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