Multiband mechanism of the pair fluctuation screening

TL;DR

This paper investigates how a multiband mechanism involving pair-exchange coupling can suppress pair fluctuations in quasi-one-dimensional superconductors, maintaining high critical temperatures even with passive higher-dimensional bands.

Contribution

It demonstrates that the multiband pair-exchange mechanism effectively screens pair fluctuations regardless of the stable condensate's parameters, including passive bands without intrinsic superconductivity.

Findings

Pair fluctuations can be suppressed by multiband coupling.

Passive higher-dimensional bands aid in fluctuation screening.

The mechanism is robust against changes in the stable condensate's properties.

Abstract

Recent chain-like structured materials have shown a robust superconducting phase. These materials exhibit the presence of quasi-one-dimensional bands (q1D) coupled to conventional higher-dimensional bands. On the mean-field level such systems have a high critical temperature when the chemical potential is close to the edge of a q1D band and the related Lifshitz transition is approached. However, the impact of the pair fluctuations compromises the mean-field results. Recently it has been demonstrated that these fluctuations can be suppressed (screened) by a specific multiband mechanism based on the pair-exchange coupling of the q1D condensate to a stable higher-dimensional one. In the present work we demonstrate that strikingly enough, this mechanism is not very sensitive to the basic parameters of the stable condensate such as its strength and dimensionality. For example, even the presence of a passive higher-dimensional band, which does not exhibit any superconducting correlations when taken as a separate superconductor, results in suppression of the pair fluctuations.