12,110 research outputs found
Vortex Softening: Origin of the second peak effect in BiSrCaCuO
Transverse ac permeability measurements in BiSrCaCuO single crystals at low fields and temperatures in a vortex configuration
free of external forces show that the decrease of the critical current as
measured by magnetization loops at the second peak effect is an artifact due to
creep. On the other hand, the increase of critical current at the second peak
is due to a genuine softening of the tilting elastic properties of vortices in
the individual pinning regime that precedes the transition to a disorder state.Comment: 4 pages, 5 figures, RevTex, two column versio
Phase Coherence Effects in the Vortex Transport Entropy
Nernst and electrical resistivity measurements in superconducting YBCO and
BSCCO with and without columnar defects show a distinctive thermodynamics of
the respective liquid vortex matter. At a field dependent high temperature
region in the phase diagram the Nernst signal is independent of structural
defects in both materials. At lower temperatures, in YBCO, defects contribute
only to the vortex mobility and the transport entropy is that of a system of
vortex lines. The transition to lower temperatures in BSCCO has a different
origin, the maximum in the Nernst signal when decreasing temperature is not
associated with transport properties but with the entropy behavior of pancake
vortices in the presence of structural defects.Comment: 4 pages, 3 figures. Accepted for publication in Physical Review
Letter
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