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

• Published in: npj quantum materials Vol. 6; no. 1
• Main Authors: Zhang, Xinyang, Hen, Bar, Palevski, Alexander, Kapitulnik, Aharon
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 19.03.2021; Nature Publishing Group
• Subjects: 639/766/119/1003; 639/766/119/2795; Broadband; Condensed Matter Physics; Couplings; Divergence; Indium; Low temperature resistance; Magnetic fields; Microwaves; Physics; Physics and Astronomy; Quantum Physics; Resistance; Robustness; Saturation; Structural Materials; Superconductivity; Surfaces and Interfaces; Thin Films; Two dimensional composites
• DOI: 10.1038/s41535-021-00329-2
• ISSN: 2397-4648

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.