From Cooper-pairs to resonating bipolarons

TL;DR

This paper explores the crossover between weak and strong coupling regimes in superconductivity, proposing a resonating bipolaron model within a Fermi sea that can lead to a superconductor-insulator transition.

Contribution

It introduces a novel scenario of resonating bipolarons in a Fermi sea, bridging the gap between amplitude and phase fluctuation regimes in superconductivity.

Findings

Resonating bipolarons can induce a superconductor-insulator transition.

The crossover regime involves competition between amplitude and phase correlations.

The model draws parallels with Feshbach resonances in ultracold gases.

Abstract

After a short review of the different physics in the weak and strong coupling regime, resulting in amplitude fluctuation controlled Cooper pair superconductivity and phase fluctuation controlled superfluidity of tightly bound local polaron pairs, we suggest a scenario for the cross-over regime between those two. It is based on the idea of resonating Bipolarons inside a Fermi sea of uncorrelated electrons, similar to the Feshbach resonance in Fermionic gases in optical traps. Due to the competition between amplitude and phase correlations such systems in the cross-over regime can exhibit a superconductor to insulator transition upon varying the strength of that resonance.