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

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.

7 pages, 5 figures and Supplemental Material (5 pages, 5 figures)

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• Cooper pairing, flat-band superconductivity and quantum geometry in the pyrochlore-Hubbard model
• Importance of dxy orbital and electron correlation in iron-based superconductors revealed by phase diagram for 1111-system
• Tunable BCS-BEC crossover, reentrant, and hidden quantum phase transitions in two-band superconductors with tunable valence and conduction bands
• Pseudogap and Strong Pairing Induced by Incipient and Shallow Bands in the Quasi-Two-Dimensional KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Emergent Fano-Feshbach resonance in two-band superconductors with an incipient quasi-flat band: Enhanced critical temperature evading particle-hole fluctuations
• Hidden Pseudogap and Excitation Spectra in a Strongly Coupled Two-Band Superfluid/Superconductor
• Towards an effective mass model for the quasi-1D magnesium diboride superconducting nanostructures
• Possibility of BCS-BEC crossover in $\kappa$-type organic superconductors
• Hidden Universal Metal in Cuprate Superconductors