Spin-orbit Coupling Effects on the Superfluidity of Fermi Gas in an Optical Lattice

TL;DR

This paper explores how spin-orbit coupling influences superfluidity in a Fermi gas within an optical lattice, revealing filling-dependent phase transitions, suppression and enhancement of superfluid properties, and novel crossover phenomena.

Contribution

It provides new insights into the effects of spin-orbit coupling on superfluidity in lattice systems, including phase transitions and modifications of superfluid characteristics.

Findings

Quantum phase transition from semimetal to superfluid at half filling with large SOC.

SOC suppresses superfluidity near half filling but enhances pairing at small fillings.

Superfluid fraction exhibits unique behaviors compared to non-lattice systems.

Abstract

We investigate the superfluidity of attractive Fermi gas in a square optical lattice with spin-orbit coupling (SOC). We show that the system displays a variety of new filling-dependent features. At half filling, a quantum phase transition from a semimetal to a superfluid is found for large SOC. Close to half filling where the emerging Dirac cones governs the behaviors of the system, SOC tends to suppress the BCS superfluidity. Conversely, SOC can significantly enhance both the pairing gap and condensate fraction and lead to a new BCS-BEC crossover for small fillings. Moreover, we demonstrate that the superfluid fraction also exhibits many interesting phenomena compared with the spin-orbit coupled Fermi gas without lattice.