Nature of the superconductor-insulator transition in disordered superconductors

TL;DR

This paper investigates the superconductor-insulator transition in disordered thin films using numerical methods, revealing how disorder and magnetic fields create inhomogeneous superconducting regions and influence the transition.

Contribution

It introduces a combined Bogoliubov-De-Gennes and Monte-Carlo approach to study the microscopic mechanisms of the transition, highlighting the role of disorder-induced superconducting islands.

Findings

Weak disorder leads to complete suppression of superconductivity with magnetic field.

Strong disorder results in persistent islands of superconductivity with phase fluctuations.

The transition mechanism involves destruction of global coherence due to island decoupling.

Abstract

As a superconducting thin film becomes disordered and subject to an increasing magnetic field, a point is reached when it undergoes a transition from a superconducting to an insulating state. We use the Bogoliubov-De-Gennes equations and a novel Monte-Carlo approach to study this transition numerically, starting from a microscopic hamiltonian. The key effect of disorder is to create 'islands' of strong superconductivity, coupled by regions that are only weakly superconducting. In the case of weak disorder, an increasing magnetic field eventually destroys the superconducting state throughout the material, leading to an insulator. On the other hand, when disorder is strong, superconductivity persists in the islands, and the effect of a magnetic field is to suppress the coupling between them, resulting in strong superconducting phase fluctuations, again leading to an insulating state. These findings may be relevant to the high-temperature superconductors, where intrinsic disorder may play a role.