Dynamical structure factors of a two-dimensional Fermi superfluid within random phase approximation

TL;DR

This paper uses RPA to numerically analyze the dynamical structure factors of a 2D Fermi superfluid, revealing the behavior of the Higgs mode and pairing excitations across the BEC-BCS crossover.

Contribution

It provides the first detailed RPA-based analysis of dynamical structure factors in 2D Fermi superfluids, highlighting the Higgs mode stability and dimensional effects.

Findings

Higgs mode is stable at small momentum in 2D Fermi superfluids.

Higgs mode visibility decreases with stronger interactions.

Signal of the Higgs mode is more prominent in 2D than in 3D.

Abstract

Based on random phase approximation (RPA), we numerically calculate dynamical structure factors of a balanced two-dimensional (2D) Fermi superfluid, and discuss their energy, momentum and interaction strength dependence in the 2D BEC-BCS crossover. At a small transferred momentum, a stable Higgs mode is observed in the unitary 2D Fermi superfluid gas where the particle-hole symmetry is not satisfied. Stronger interaction strength will make the visibility of the dispersion of Higgs mode harder to be observed. We also discuss the dimension effect and find that the signal of the Higgs mode in two dimension is more obvious than that in 3D case. At a large transferred momentum regime, stronger interaction strength will induce the weight of the molecules excitation increasing, while in verse the atomic one decreasing, which shows the pairing information of Fermi superfluid. The theoretical results qualitatively agree with the corresponding Quantum Monte Carlo data.