Screening of pair fluctuations in superconductors with coupled shallow and deep bands: a route to higher temperature superconductivity

TL;DR

This paper proposes a multiband superconductivity mechanism combining shallow and deep bands with Josephson coupling to enhance critical temperature and suppress fluctuations, offering a promising route to higher-temperature superconductors.

Contribution

It introduces a novel multicomponent superconductivity regime with coupled shallow and deep bands that stabilizes high Tc by screening fluctuations.

Findings

Efficient fluctuation suppression even with weak inter-band coupling.

Coexistence of BCS and BCS-BEC crossover regimes enhances Tc.

Multiband coupling stabilizes superconductivity against fluctuations.

Abstract

A combination of strong Cooper pairing and weak superconducting fluctuations is crucial to achieve and stabilize high-Tc superconductivity. We demonstrate that a coexistence of a shallow carrier band with strong pairing and a deep band with weak pairing, together with the Josephson-like pair transfer between the bands to couple the two condensates, realizes an optimal multicomponent superconductivity regime: it preserves strong pairing to generate large gaps and a very high critical temperature but screens the detrimental superconducting fluctuations, thereby suppressing the pseudogap state. Surprisingly, we find that the screening is very efficient even when the inter-band coupling is very small. Thus, a multi-band superconductor with a coherent mixture of condensates in the BCS regime (deep band) and in the BCS-BEC crossover regime (shallow band) offers a promising route to higher critical temperatures.