Topological superfluid phases of attractive Fermi-Hubbard model in narrow-band cold-atom optical lattices

TL;DR

This paper explores how attractive interactions in a narrow-band, spin-orbit coupled Fermi-Hubbard model lead to various topological superfluid phases, with the topological gap maximized at specific parameter regimes in cold atom optical lattices.

Contribution

It identifies the phase diagram and optimal parameters for topological superfluid phases in a narrow-band Fermi-Hubbard model with Rashba SOC and Zeeman field.

Findings

Topological superfluid phases depend on chemical potential and Zeeman field.

Maximum topological gap is about 10-12.5% of interaction strength.

Narrow-band effects enhance the topological gap under certain conditions.

Abstract

We investigate the effects of attractive Hubbard interaction on two-component fermionic atoms in narrow two-dimensional (2D) energy bands that exhibit Rashba spin-orbit coupling (SOC) in the presence of an applied Zeeman field. This narrow-band 2D spin-orbit coupled attractive Fermi-Hubbard model can potentially be realized in cold atom systems in optical lattices with artificially engineered Rashba SOC and Zeeman field. Employing a self-consistent mean field approximation for the pairing potential, we uncover a complex phase diagram featuring various topological superfluid (TS) phases, dependent on the chemical potential and the Zeeman field. We focus on the pairing potential and the corresponding quasiparticle gap characterizing the TS phases, which are notably small for a wide-band model with quadratic dispersion near the $\Gamma$-point, as found in earlier work, and we identify the parameter regimes that maximize the gap. We find that, while generally the value of the pairing potential increases with the reduction of the fermionic bandwidth, as expected for narrow- or flat-band systems, the magnitude of the topological gap characterizing the TS phases reaches a maximum of about $10-12.5\%$ of the interaction strength at finite values of the hopping amplitude, Rashba coupling, and Zeeman field.