Strongly fluctuating fermionic superfluid in the attractive $\ensuremath{\pi}$-flux Hubbard model

Strongly fluctuating fermionic superfluid in the attractive $π$ -flux Hubbard model

Ya-Jie Wu, Jiang Zhou, and Su-Peng Kou

Phys. Rev. A 89, 013619 – Published 22 January 2014

Abstract

Ultracold atoms in an optical lattice provide a platform for realization of the superfluid (SF) state, a quantum order with paired charge-neutral fermions. In this paper, we study the SF state in the two-dimensional attractive Hubbard model with $π$ flux on each plaquette. The SF state in the $π$ -flux lattice model suffers very strong quantum fluctuations and the ground state becomes a possible quantum phase liquid state. In this phase, there exists Cooper pairing together with a finite energy gap for the atoms, but no long-range SF phase coherence exists at zero temperature. In addition, we discuss the properties of the SF vortices.