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.
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
G
G
Bridoux
G
G
Nieva
F
F
de la Cruz