Phase Coherence Effects in the Vortex Transport Entropy

TL;DR

This paper investigates how phase coherence influences vortex transport entropy in high-temperature superconductors YBCO and BSCCO, revealing defect-independent thermodynamics at high temperatures and defect-related effects at lower temperatures.

Contribution

It provides new insights into the thermodynamic behavior of vortex matter, distinguishing defect effects in YBCO and BSCCO across temperature regimes.

Findings

High-temperature Nernst signal is defect-independent in both materials.

Defects affect vortex mobility but not transport entropy in YBCO.

In BSCCO, the Nernst maximum relates to pancake vortex entropy, not transport properties.

Abstract

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.