508 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
Slow Crack Propagation in Heterogeneous Materials
Statistics and thermally activated dynamics of crack nucleation and
propagation in a two-dimensional heterogeneous material containing quenched
randomly distributed defects are studied theoretically. Using the generalized
Griffith criterion we derive the equation of motion for the crack tip position
accounting for dissipation, thermal noise and the random forces arising from
the defects. We find that aggregations of defects generating long-range
interaction forces (e.g., clouds of dislocations) lead to anomalously slow
creep of the crack tip or even to its complete arrest. We demonstrate that
heterogeneous materials with frozen defects contain a large number of arrested
microcracks and that their fracture toughness is enhanced to the experimentally
accessible time scales.Comment: 5 pages, 1 figur
Depinning of a vortex chain in a disordered flow channel
We study depinning of vortex chains in channels formed by static, disordered
vortex arrays. Depinning is governed either by the barrier for defect
nucleation or for defect motion, depending on whether the chain periodicity is
commensurate or incommensurate with the surrounding arrays. We analyze the
reduction of the gap between these barriers as function of disorder. At large
disorder, commensurability becomes irrelevant and the pinning force is reduced
to a small fraction of the ideal shear strength of ordered channels.
Implications for experiments on channel devices are discussed.Comment: 5 pages, 4 figures. Accepted for publication in Europhysics Letter
Spectral flow in superconducting point contacts
We find that multiple Andreev reflections mediating the transport in
superconducting point contacts are strongly affected by a small amount of
impurities in the area of the contact. We also argue that the model based on
Zener transitions within independent conducting channels is not suitable for
kinetic processes in multichannel contacts.Comment: Revised version. To be published in Europhysics Letter
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