Universal bound to the amplitude of the vortex Nernst signal in superconductors

TL;DR

This study reveals a universal upper limit to the vortex Nernst signal amplitude in superconductors, regardless of their critical temperature or magnetic field, linked to a fundamental entropy per vortex per layer.

Contribution

It demonstrates a universal bound on the vortex Nernst signal amplitude across different superconductors, connecting it to a fundamental entropy per vortex per layer.

Findings

The Nernst signal magnitude aligns with theoretical expectations in STO.

The peak vortex Nernst amplitude is similar across various superconductors.

Maximum Nernst signal corresponds to an entropy of approximately k_B ln 2 per vortex per layer.

Abstract

A liquid of superconducting vortices generates a transverse thermoelectric response. This Nernst signal has a tail deep in the normal state due to superconducting fluctuations. Here, we present a study of the Nernst effect in two-dimensional hetero-structures of Nb-doped strontium titanate (STO) and in amorphous MoGe. The Nernst signal generated by ephemeral Cooper pairs above the critical temperature has the magnitude expected by theory in STO. On the other hand, the peak amplitude of the vortex Nernst signal below $T_c$ is comparable in both and in numerous other superconductors despite the large distribution of the critical temperature and the critical magnetic fields. In four superconductors belonging to different families, the maximum Nernst signal corresponds to an entropy per vortex per layer of $\approx$ k$_Bln2$.