Onset of Nernst Effect Beyond the Coherence Critical Field of a Nano-Scale Granular Superconductor

TL;DR

This study investigates the Nernst effect in granular aluminum films near the metal-insulator transition, revealing a peak in the Nernst signal associated with entropy transport after superconducting coherence loss.

Contribution

It provides new insights into the behavior of the Nernst effect beyond the coherence critical field in nano-scale granular superconductors.

Findings

Nernst signal peaks at a field where resistance is nearly restored.

Fluctuation paraconductivity scales with the Nernst signal above T_c.

Sharp transitions observed in magneto-resistance and Nernst effect.

Abstract

We report measurements of the Nernst effect and of the magneto-resistance 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.