A length scale for the superconducting Nernst signal above T$_{c}$ in Nb$_{0.15}$Si$_{0.85}$

TL;DR

This study identifies a universal length scale governing the Nernst signal above T_c in amorphous NbSi films, showing it is driven by transient Cooper pairs across wide temperature and field ranges.

Contribution

It introduces a unified function describing the Nernst coefficient based on the correlation length, highlighting the role of short-lived Cooper pairs in the Nernst effect.

Findings

Nernst coefficient exhibits two regimes separated by a characteristic field scale.

A single function F(ξ) describes the Nernst response across different regimes.

The Nernst signal is solely due to short-lived Cooper pairs over a broad temperature and field range.

Abstract

We present a study of the Nernst effect in amorphous superconducting thin films of Nb$_{0.15}$Si$_{0.85}$. The field dependence of the Nernst coefficient above T$_{c}$ displays two distinct regimes separated by a field scale set by the Ginzburg-Landau correlation length. A single function $F(\xi)$, with the correlation length as its unique argument set either by the zero-field correlation length (in the low magnetic field limit) or by the magnetic length (in the opposite limit), describes the Nernst coefficient. We conclude that the Nernst signal observed on a wide temperature ($30 \times T_c$) and field ($4 \times B_{c2}$) range is exclusively generated by short-lived Cooper pairs.