Anomalous metallic state above the upper critical field of the conventional three-dimensional superconductor AgSnSe2 with strong intrinsic disorder

TL;DR

This study investigates AgSnSe2, a strongly disordered 3D superconductor, revealing an anomalous metallic state above the upper critical field likely due to quantum phase fluctuations.

Contribution

It uncovers the existence of an anomalous metallic state above the upper critical field in a strongly disordered 3D superconductor, which is a novel observation.

Findings

Resistive transition broadens near zero temperature.

Anomalous metallic state exists above the thermodynamic upper critical field.

Quantum phase fluctuations may cause this metallic state.

Abstract

We report superconducting properties of AgSnSe2 which is a conventional type-II superconductor in the very dirty limit due to intrinsically strong electron scatterings. While this material is an isotropic three-dimensional (3D) superconductor with a not-so-short coherence length where strong vortex fluctuations are NOT expected, we found that the magnetic-field-induced resistive transition at fixed temperatures becomes increasingly broader toward zero temperature and, surprisingly, that this broadened transition is taking place largely ABOVE the upper critical field determined thermodynamically from the specific heat. This result points to the existence of an anomalous metallic state possibly caused by quantum phase fluctuations in a strongly-disordered 3D superconductor.