Fluctuations and the resistive transition in paramagnetically limited superconductors

We have studied, both theoretically and experimentally, the extra conductivity ${\sigma }_{\mathrm{fl}}$ due to thermal fluctuations in high-field superconductors in the Pauli-paramagnetic limit (SPPL). We first investigate theoretically the Aslamazov-Larkin (AL) term, and show that the Pauli-paramagnetic effect in the AL term can be included by renormalizing the thickness of the film. Then we calculate the pair-breaking function for the Maki-Thompson (MT) term in a magnetic field within the lowest-order approximation of Keller and Korenman and show that in contrast to ordinary superconductors the MT term in SPPL can be enhanced by a weak parallel field. We also report the first experimental measurements of ${\sigma }_{\mathrm{fl}}$ in SPPL. The angular dependence of the AL term is found to be essentially in agreement with the calculation of Aoi reported earlier. Near $T_{c0}$ the MT term is observed to be suppressed by a parallel field. We also study the effect of a perpendicular field, and find, both theoretically and experimentally, that in SPPL the MT term appears to be suppressed by a perpendicular field.