Molecule and polaron in a highly polarized two-dimensional Fermi gas with spin-orbit coupling

TL;DR

This paper explores how spin-orbit coupling induces pairing and phase transitions in a highly polarized two-dimensional Fermi gas, revealing novel molecular and polaron states and their transitions, with implications for topological superfluidity.

Contribution

It demonstrates the emergence of pairing instability and phase transitions in a polarized 2D Fermi gas with SOC, including molecular, polaron, and superfluid states, extending understanding of such systems.

Findings

SOC induces pairing instability at all interaction strengths.

First-order transition from FFLO-like molecular state to zero-momentum pairing state.

Existence of a polaron-molecule transition indicating a phase change between superfluid and normal states.

Abstract

We show that spin-orbit coupling (SOC) gives rise to pairing instability in a highly polarized two-dimensional Fermi gas for arbitrary interaction strength. The pairing instability can lead to a Fulde-Ferrell-Larkin-Ovchinnikov-like molecular state, which undergoes a first-order transition into a pairing state with zero center-of-mass momentum as the parameters are tuned. These pairing states are metastable against a polaron state dressed by particle-hole fluctuations for small SOC. At large SOC, a polaron-molecule transition exists, which suggests a phase transition between the topological superfluid state and the normal state for a highly polarized Fermi gas in the thermodynamic limit. As polarization in a Fermi gas with SOC is induced by the effective Zeeman field, we also discuss the influences of the effective Zeeman field on the ground state of the system. Our findings may be tested directly in future experiments.