Resonant Superfluidity in an Optical Lattice

TL;DR

This paper investigates ultracold fermionic atoms in an optical lattice near a Feshbach resonance, revealing a phase transition to a Mott insulator and analyzing the BEC/BCS crossover and critical temperature behavior.

Contribution

It introduces a multi-band Bose-Fermi Hubbard model with a self-consistent mean-field approach and solves it using Generalized Dynamical Mean-Field Theory, highlighting new phase transitions.

Findings

Identification of a fermionic Mott insulator transition at half filling.

Calculation of the BEC/BCS crossover and critical temperature behavior.

Minimal critical temperature at resonance.

Abstract

We study a system of ultracold fermionic Potassium (40K) atoms in a three-dimensional optical lattice in the vicinity of an s-wave Feshbach resonance. Close to resonance, the system is described by a multi-band Bose-Fermi Hubbard Hamiltonian. We derive an effective lowest-band Hamiltonian in which the effect of the higher bands is incorporated by a self-consistent mean-field approximation. The resulting model is solved by means of Generalized Dynamical Mean-Field Theory. In addition to the BEC/BCS crossover we find a phase transition to a fermionic Mott insulator at half filling, induced by the repulsive fermionic background scattering length. We also calculate the critical temperature of the BEC/BCS-state and find it to be minimal at resonance.