Nernst effect beyond the coherence critical field of a nanoscale granular superconductor

Abstract

We report measurements of the Nernst effect and of the magnetoresistance of granular aluminum films near the metal-to-insulator transition. These films show sharp transitions as a function of temperature and magnetic field. At low temperatures the Nernst signal displays a sharp peak at a field where more than 90% of the normal-state resistance has been restored, suggesting a transition involving entropy transport after superconducting coherence has been destroyed. At temperatures higher than the critical temperature the fluctuation paraconductivity scales with the Nernst signal, in agreement with a description in terms of fluctuations of the order parameter.