804 research outputs found
The strengthening of reentrant pinning by collective interactions in the peak effect
Since it was first observed about 40 years ago [1], the peak effect has been
the subject of numerous research mainly impelled by the desire to determine its
exact mechanisms. Despite these efforts, a consensus on this question has yet
to be reached. Experimentally, the peak effect indicates a transition from a
depinned vortex phase to a reentrant pinning phase at high magnetic field. To
study the effects of intrinsic pinning on the peak effect, we consider
FeNiZr superconducting metallic glasses in which the vortex
pinning force varies depending on the Fe content and in which a huge peak
effect is seen as a function of magnetic field. The results are mapped out as a
phase diagram in which it is readily seen that the peak effect becomes broader
with decreasing pinning force. Typically, pinning can be understood by
increased pinning centers, but here, we show that reentrant pinning is due to
the strengthening of interactions (while decreasing pinning strength). Our
results demonstrate the strengthening of the peak effect by collective effects.Comment: 4 pages, 4 figure
Localization Properties of the Periodic Random Anderson Model
We consider diagonal disordered one-dimensional Anderson models with an
underlying periodicity. We assume the simplest periodicity, i.e., we have
essentially two lattices, one that is composed of the random potentials and the
other of non-random potentials. Due to the periodicity special resonance
energies appear, which are related to the lattice constant of the non-random
lattice. Further on two different types of behaviors are observed at the
resonance energies. When a random site is surrounded by non-random sites, this
model exhibits extended states at the resonance energies, whereas otherwise all
states are localized with, however, an increase of the localization length at
these resonance energies. We study these resonance energies and evaluate the
localization length and the density of states around these energies.Comment: 4 page
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