Superfluid phases of ultracold Fermi gases on a checkerboard superlattice

TL;DR

This paper investigates the phase diagram of ultracold Fermi gases in a checkerboard superlattice, revealing a preference for 0-phase superfluidity, a quantum phase transition at half filling, and a transition to a checkerboard insulator with increasing potential.

Contribution

It introduces a two-band superfluid model for Fermi gases in a checkerboard lattice and analyzes the phase transitions and order parameters using mean-field theory.

Findings

System prefers 0-phase solutions over π-phase.

Quantum phase transition from superfluid to normal state at half filling.

Normal state transitions into a checkerboard insulator as potential increases.

Abstract

We analyze the ground-state phase diagram of two-component Fermi gases loaded into a two-dimensional checkerboard superlattice, i.e. a double-well optical lattice, potential within the BCS mean-field theory. We show that, by coupling the two s-wave sublattice superfluid order parameters, a checkerboard potential gives rise to a Hamiltonian that has the form of a two-band superfluidity with three (two intraband and an interband) nonlocal order parameters. We study the evolution of these order parameters as a function of particle filling, interaction strength and checkerboard potential, and find that the system always prefers the 0-phase solutions, i.e. the phase difference between sublattice order parameters is 0, but never the $\pi$-phase one. In addition, we find that the ground-state of the system undergo a superfluid-normal quantum phase transition at half fillings beyond a critical checkerboard potential $C$, the threshold of which is precisely determined by the magnitude of the order parameter at $C = 0$, and that the normal state rapidly turns into a checkerboard insulator as $C$ increases.