Localized Superconductivity in the Quantum-Critical Region of the Disorder-Driven Superconductor-Insulator Transition in TiN Thin Films

TL;DR

This study explores the transition between superconducting and insulating states in TiN thin films, revealing localized Cooper pairs and a sharp phase boundary without an intermediate metallic phase.

Contribution

It provides new insights into the nature of the superconductor-insulator transition, highlighting the formation of a collective localized Cooper pair state in TiN films.

Findings

Sharp superconductor-insulator phase boundary

Thermally activated conductivity in insulating films

Zero-conductivity state destroyed at depinning threshold

Abstract

We investigate low-temperature transport properties of thin TiN superconducting films in the vicinity of the disorder-driven superconductor-insulator transition. In a zero magnetic field, we find an extremely sharp separation between superconducting and insulating phases, evidencing a direct superconductor-insulator transition without an intermediate metallic phase. At moderate temperatures, in the insulating films we reveal thermally activated conductivity with the magnetic field-dependent activation energy. At very low temperatures, we observe a zero-conductivity state, which is destroyed at some depinning threshold voltage V_T. These findings indicate formation of a distinct collective state of the localized Cooper pairs in the critical region at both sides of the transition.