Mechanism of screening or enhancing the pseudogap throughout the two-band Bardeen-Cooper-Schrieffer to Bose-Einstein condensate crossover

TL;DR

This paper explores how multiple pseudogaps form and evolve in two-band fermionic systems during the BCS-BEC crossover, highlighting the roles of screening effects and pair-exchange couplings, with implications for iron-based superconductors.

Contribution

It reveals the mechanism of multiple pseudogap formation driven by pair-exchange couplings and screening effects in two-band systems across the BCS-BEC crossover, a novel insight into pseudogap phenomenology.

Findings

Multiple pseudogaps exhibit a rise-and-fall behavior during the crossover.

Screening effects suppress pseudogap formation in the shallow band at small pair-exchange couplings.

Binary preformed Cooper pairs emerge from intra-band and pair-exchange interactions.

Abstract

We demonstrate the rise-and-fall of multiple pseudogaps in the Bardeen-Cooper-Schrieffer-Bose-Einstein-condensation (BCS-BEC) crossover in two-band fermionic systems having different pairing strengths in the deep band and in the shallow band. The striking features of this phenomenon are an unusual many-body screening of pseudogap state and the importance of pair-exchange couplings, which induces multiple pseudogap formation in the two bands. The multi-band configuration suppresses pairing fluctuations and the pseudogap opening in the strongly-interacting shallow band at small pair-exchange couplings by screening effects, with possible connection to the pseudogap phenomenology in iron based superconductors. On the other hand, the multiple pseudogap mechanism accompanies with the emergence of binary preformed Cooper pairs originating from interplay between intra-band and pair-exchange couplings.