Superconductor-insulator transition in Coulomb disorder

TL;DR

This paper investigates the superconductor-insulator transition driven by electron concentration in a Coulomb-disordered system, analyzing how screening and localization influence phase boundaries, with findings relevant to the BEC-BCS crossover.

Contribution

It introduces a self-consistent model for the superconductor-insulator transition considering Coulomb disorder and screening effects on electrons and Cooper pairs.

Findings

The phase boundary between superconductor and insulator is mapped in electron concentration and pair size.

For strong disorder, the transition line aligns with the BEC-BCS crossover.

Both electrons and Cooper pairs can be delocalized or localized depending on parameters.

Abstract

Superconductor-insulator transition driven by the decreasing concentration of electrons $n$ is studied in the case of the disorder potential created by randomly positioned charged impurities. Electrons and Cooper pairs (formed by an non-Coulomb attraction) nonlinearly screen the random potential of impurities. Both electrons and Cooper pairs can be delocalized or localized in the resulting self-consistent potential. The border separating the superconductor and insulator phases in the plane of the concentration of electrons and the length of the Cooper pair is found. For a strong disorder the central segment of this border follows the BEC-BCS crossover line defined for a clean sample.