Recent experimental studies on strongly disordered indium oxide films have revealed an unusual first-order quantum phase transition between the superconducting and insulating states (SIT). This transition is characterized by a discontinuous jump from non-zero to zero values of superfluid stiffness at the critical point, contradicting the conventional "scaling scenario" typically associated with SIT. In this paper, we present a theoretical framework for understanding this first-order transition. Our approach is based on the concept of competition between two fundamentally distinct ground states that arise from electron pairs initially localized by strong disorder: the superconducting state and the Coulomb glass insulator. These ground states are distinguished by two crucially different order parameters, suggesting a natural expectation of a discontinuous transition between them at T=0. This transition occurs when the magnitudes of the superconducting gap Δ and the Coulomb gap EC become comparable. Additionally, we extend our analysis to low non-zero temperatures and provide a mean-field "phase diagram" in the plane of (T/Δ,EC/Δ). Our results reveal the existence of a natural upper bound for the kinetic inductance of strongly disordered superconductors.
@article{arxiv.2405.08571,
title = {Mean-field theory of first-order quantum superconductor-insulator transition},
author = {Igor Poboiko and Mikhail Feigel'man},
journal= {arXiv preprint arXiv:2405.08571},
year = {2024}
}