Evidence for a universal minimum superfluid response in field-tuned disordered superconducting films measured using low frequency ac conductivity

TL;DR

This study reveals a universal minimum superfluid response in disordered superconducting films near the transition, observed through low frequency ac conductivity, consistent across different materials and matching BKT transition predictions.

Contribution

It provides experimental evidence for a universal superfluid density threshold at the superconductor-insulator transition in disordered films, linking it to BKT physics.

Findings

Universal superfluid density drop at transition

Consistent critical exponent with previous studies

Universal behavior observed across different materials

Abstract

Our measurements of the low frequency ac conductivity in strongly disordered two-dimensional films near the magnetic field-tuned superconductor-to-insulator transition show a sudden drop in the phase stiffness of superconducting order with either increased temperature or magnetic field. Surprisingly, for two different material systems, the abrupt drop in the superfluid density in a magnetic field has the same universal value as that expected for a Berezinskii-Kosterlitz-Thouless transition in zero magnetic field. The characteristic temperature at which phase stiffness is suddenly lost can be tuned to zero at a critical magnetic field, following a power-law behavior with a critical exponent consistent with that obtained in previous dc transport studies on the dissipative side of the transition.