Nernst effect as a probe of superconducting fluctuations in disordered thin films

Abstract

In amorphous superconducting thin films of $Nb_{0.15}Si_{0.85}$ and $InO_x$,\na finite Nernst coefficient can be detected in a wide range of temperature and\nmagnetic field. Due to the negligible contribution of normal quasi-particles,\nsuperconducting fluctuations easily dominate the Nernst response in the entire\nrange of study. In the vicinity of the critical temperature and in the\nzero-field limit, the magnitude of the signal is in quantitative agreement with\nwhat is theoretically expected for the Gaussian fluctuations of the\nsuperconducting order parameter. Even at higher temperatures and finite\nmagnetic field, the Nernst coefficient is set by the size of superconducting\nfluctuations. The Nernst coefficient emerges as a direct probe of the ghost\ncritical field, the normal-state mirror of the upper critical field. Moreover,\nupon leaving the normal state with fluctuating Cooper pairs, we show that the\ntemperature evolution of the Nernst coefficient is different whether the system\nenters a vortex solid, a vortex liquid or a phase-fluctuating superconducting\nregime.\n