Thermally Fluctuating Inhomogeneous Superfluid State of Strongly Interacting Fermions in an Optical Lattice

TL;DR

This paper investigates the intermediate temperature regime of strongly interacting fermions in an optical lattice, revealing fluctuating superfluid domains with strong pairing correlations that are experimentally observable.

Contribution

It introduces a new Monte Carlo method to study inhomogeneous superfluid states and maps their thermal evolution in a trapped two-dimensional fermion Hubbard model.

Findings

Presence of large pairing amplitude domains at intermediate temperatures

Spectral signatures of inhomogeneous superfluid states

Thermal evolution of density and pairing correlations

Abstract

The presence of attractive interaction between fermions can lead to pairing and superfluidity in an optical lattice. The temperature needed to observe superfluidity is about a tenth of the tunneling energy in the optical lattice, and currently beyond experimental reach. However, at strong coupling the precursors to global superfluidity should be visible at achievable temperatures, in terms of fluctuating domains with strong pairing correlations. We explore this regime of the attractive two dimensional fermion Hubbard model, in the presence of a confining potential, using a new Monte Carlo technique. We capture the low temperature inhomogeneous superfluid state with its unusual spectral signatures but mainly focus on the experimentally accessible intermediate temperature state. In this regime, and for the trap center density we consider, there is a large pairing amplitude at the center, spatially correlated into domains extending over several lattice spacings. We map out the thermal evolution of the local density, the double occupancy, the pairing correlations, and the momentum distribution function across this phase fluctuation window.