Reentrant BCS-BEC crossover and a superfluid-insulator transition in optical lattices

Abstract

We study thermodynamics of a two-species Feshbach-resonant atomic Fermi gas in a periodic potential, focusing in a deep optical potential where a tight binding model is applicable. We show that for more than half-filled band the gas exhibits a reentrant crossover with decreased detuning (increased attractive interaction), from a paired BCS superfluid to a Bose-Einstein condensate (BEC) of molecules of holes, back to the BCS superfluid, and finally to a conventional BEC of diatomic molecules. This behavior is associated with the non-monotonic dependence of the chemical potential on detuning and the concomitant Cooper-pair/molecular size, larger in the BCS and smaller in the BEC regimes. For a single filled band we find a quantum phase transition from a band insulator to a BCS-BEC superfluid, and map out the corresponding phase diagram.

5 pages, 2 figures

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• Extended molecules and geometric scattering resonances in optical lattices
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• Dynamic properties of superconductors: Anderson-Bogoliubov mode and Berry phase in BCS and BEC regimes
• Spin-orbit-induced bound state and molecular signature of the degenerate Fermi gas in a narrow Feshbach resonance
• On the Boson-Fermion resonant model on a lattice
• Manipulating Cooper pairs with a controllable momentum in periodically driven degenerate Fermi gases
• Fulde-Ferrell superfluids in spinless ultracold Fermi gases
• One-dimensional model of chiral fermions with Feshbach resonant interactions
• Spin-orbit coupled repulsive Fermi atoms in a one-dimensional optical lattice
• Vorticity-Crystalline Order Coupling in Supersolids: Excitations and Re-entrant Phases