Robust anomalous metallic states and vestiges of self duality in two-dimensional granular In-InOx composites

TL;DR

This study investigates the anomalous metallic states in granular In-InOx composites, revealing how inhomogeneities and external noise influence the superconductor-insulator transition and suggest vestiges of duality in the system.

Contribution

It demonstrates the role of granularity and external noise in stabilizing metallic states and uncovers evidence of emergent duality near the transition in a two-dimensional granular system.

Findings

Resistance saturation observed over a wide magnetic field range.

External noise and microwave radiation enhance superconductivity.

Logarithmic divergence of resistance indicates vestiges of duality.

Abstract

Many experiments investigating magnetic field tuned superconductor-insulator transition (H-SIT), often exhibit low-temperature resistance saturation, which is interpreted as an anomalous metallic phase emerging from a "failed superconductor," thus challenging conventional theory. Here we study a random granular array of indium islands grown on a gateable layer of indium-oxide. By tuning the intergrain couplings, we reveal a wide range of magnetic fields where resistance saturation is observed, under conditions of careful electromagnetic filtering and within a wide range of linear response. Exposure to external broadband noise or microwave radiation is shown to strengthen the tendency of superconductivity, where at low field a global superconducting phase is restored. Increasing magnetic field unveils an "avoided H-SIT," that exhibits granularity-induced logarithmic divergence of the resistance/conductance above/below that transition, pointing to possible vestiges of the original emergent duality observed in a true H-SIT. We conclude that anomalous metallic phase is intimately associated with inherent inhomogeneities, exhibiting robust behavior at attainable temperatures for strongly granular two-dimensional systems.