Ground state properties of a two dimensional Fermi superfluid with an anisotropic spin-orbit coupling

TL;DR

This paper theoretically explores the ground state of a 2D Fermi superfluid with anisotropic spin-orbit coupling, revealing non-monotonic density of states behavior and topological phase transitions influenced by Zeeman fields.

Contribution

It provides new insights into how anisotropic SOC affects pairing, density of states, and topological phases in 2D Fermi superfluids, including analytical results for topological invariants.

Findings

Gap parameter decreases with increasing anisotropic SOC.

Density of states exhibits non-monotonic behavior as SOC anisotropy increases.

Topological phase transition characterized by a change in the ground state wave-function.

Abstract

We performed a theoretical investigation on the ground state properties of a two dimensional ultra-cold Fermi superfluid with an anisotropic spin-orbit coupling (SOC). In the absence of Zeeman field, the system evolves from weak coupling BCS regime to strongly interacting BEC regime (BCS-BEC crossover) with increasing either the two-particle interaction strength or SOC parameters. We focused on the behaviors of pairing parameter and density of states (DOS) when increasing the anisotropic parameter of the SOC. Surprisingly, we discovered that the gap parameter decreases with increasing the anisotropic parameters, but the DOS at the Fermi surface shows non-monotonic behavior as a function of the anisotropic parameter. In the presence of the Zeeman field, we discussed a particular type of topological phase transition by obtaining the analytical result of the topological invariant and directly related this quantum phase transition with a sudden change of the ground state wave-function. Effects of higher partial wave pairing terms on this topological phase transition were briefly discussed.