Anomalous pseudogap in population imbalanced Fermi superfluids

Abstract

Abstract: In a Fermi superfluid increasing population imbalance leads initially to reduction of thetransition temperature, then the appearance of modulated Fulde-Ferrell-Larkin-Ovchinnikov(FFLO) states, and finally the suppression of pairing itself. We have carried out adetailed investigation of the spectral behavior of the imbalanced Fermi system and observeintriguing subgap features in the low polarization regime, and a re-entrant pseudogapstate at large polarization. These weak imbalance and strong imbalance features bothinvolve effects well beyond mean field theory. We establish them by using a Monte Carlotechnique on large lattices, motivate the results in terms of the pairing fielddistribution, and compare them to spectroscopic results in the imbalanced unitary Fermigas. Graphical abstract: [Figure not available: see fulltext.]