Quantum phase transition in superconducting Au0.7In0.3 films of very low normal-state sheet resistance

TL;DR

This study observes a quantum phase transition in Au0.7In0.3 films with very low resistance, switching from superconducting to metallic state under a parallel magnetic field, highlighting complex interplay between superconductivity and metallic behavior.

Contribution

It reports the first observation of a magnetic-field-tuned quantum phase transition in low-resistance AuIn films and models the system as a network of SNS junctions revealing the nature of the metallic state.

Findings

Quantum phase transition observed at low resistance levels.

Metallic state characterized by superconducting grains without Josephson coupling.

Discussion on phase fluctuations and alternative mechanisms driving the transition.

Abstract

We report the observation of a quantum phase transition (QPT), tuned by a parallel magnetic field, between a superconducting and metallic state in Au0.7In0.3 films of very low normal-state sheet resistance (< 90 Ohms). These films can be modeled as a random array of superconductor-normal metal-superconductor (SNS) junctions. Electrical transport and tunneling measurements suggest that, in the metallic state, the film consists of superconducting In-rich grains not linked by Josephson coupling. Whether phase fluctuation, which is not expected to be strong in such an SNS junction system according to the phase-number uncertainty relation, or a different physical process drives the observed QPT is discussed.