Phase-coherence effects in vortex transport entropy.
Nernst and electrical resistivity measurements in superconducting YBa2Cu3O7-delta and Bi2Sr2CaCu2O8+delta with and without columnar defects show a distinctive thermodynamics of the respective liquid vortex matter. At a field-dependent high temperature region in the H-T phase diagram, the Nernst signal is independent of structural defects in both materials. At lower temperatures, in YBa2Cu3O7-delta, 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 Bi2Sr2CaCu2O8+delta 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.
Bridoux
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Centro Atómico Bariloche and Instituto Balseiro, Comisión Nacional de Energía Atómica, Avenida E. Bustillo 9500, R84002AGP S. C. de Bariloche, Argentina. bridoux@cabbat1.cnea.gov.ar
Nieva
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de la Cruz
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