50,329 research outputs found
Critical state analysis of orthogonal flux interactions in pinned superconductors
We show that, based on the critical state model for flux-line pinning in hard
superconductors, one can assess the magnetic moment relaxation induced by the
oscillations of a perpendicular magnetic field. Our theory follows a recent
proposal of using phenomenological 2D modeling for the description of crossed
field dynamics in high-T superconductors [{\tt arXiv:cond-mat/0703330}].
Stationary regimes with either saturation to metastable configurations, or
complete decay to the thermodynamic equilibrium are obtained. The transition
between both types of response is related to the disappearance of a flux free
core within the sample. As a common feature, a step-like dependence in the time
relaxation is predicted for both cases. The theory may be applied to long bars
of arbitrary and non homogeneous cross section, under in-plane magnetic field
processes.Comment: 11 figures, submitte
Scattering approach to fidelity decay in closed systems and parametric level correlations
This paper is based on recent work which provided an exact analytical
description of scattering fidelity experiments with a microwave cavity under
the variation of an antenna coupling [K\"ober et al., Phys. Rev. E 82, 036207
(2010)]. It is shown that this description can also be used to predict the
decay of the fidelity amplitude for arbitrary Hermitian perturbations of a
closed system. Two applications are presented: First, the known result for
global perturbations is re-derived, and second, the exact analytical expression
for the perturbation due to a moving S-wave scatterer is worked out. The latter
is compared to measured data from microwave experiments, which have been
reported some time ago. Finally, we generalize an important relation between
fidelity decay and parametric level correlations to arbitrary perturbations.Comment: 20 pages, 2 figures, research article, (v2: stylistic changes, ref.
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