Density of States, Entropy, and the Superconducting Pomeranchuk Effect in Pauli-Limited Al Films

TL;DR

This study investigates the density of states and entropy in Pauli-limited aluminum films, revealing a high entropy superconducting phase with reentrant critical field behavior linked to the Pomeranchuk effect, supported by experimental and theoretical analysis.

Contribution

It demonstrates the existence of a high entropy superconducting phase in thin Al films and analyzes its properties and deviations from theory near the transition.

Findings

Reentrant parallel critical field transition observed in 6-7 nm Al films.

High entropy superconducting phase characterized by excess states near Fermi energy.

Theoretical models fit well below transition but deviate near the critical point due to electron-electron interactions.

Abstract

We present low temperature tunneling density of states measurements of Pauli-limited Al films in which the Zeeman and orbital contributions to the critical field are comparable. We show that films in the thickness range of 6-7 nm exhibit a reentrant parallel critical field transition which is associated with a high entropy superconducting phase, similar to the high entropy solid phase of 3He responsible for the Pomeranchuk effect. This phase is characterized by an excess of states near the Fermi energy so long as the parallel critical field transition remains second order. Theoretical fits to the zero bias tunneling conductance are in good agreement with the data well below the transition but theory deviates significantly near the transition. The discrepancy is a consequence of the emergence of e-e interaction correlations as one enters the normal state.