Dynamic structure factor of one-dimensional Fermi superfluid with spin-orbit coupling

TL;DR

This paper theoretically investigates the dynamic structure factor of a one-dimensional Fermi superfluid with spin-orbit coupling, revealing unique excitations and a roton-like mode associated with topological phase transition.

Contribution

It introduces a detailed theoretical analysis of the dynamic structure factor in a 1D Fermi superfluid with spin-orbit coupling, highlighting new excitation features and a topological phase transition signature.

Findings

Identification of four single-particle excitation types.

Observation of a roton-like collective mode in the topological phase.

Detection of cross single-particle excitations at small momentum.

Abstract

We theoretically calculate the density dynamic structure factor of one-dimensional Fermi superfluid with Raman-type spin-orbit coupling, and analyze its main dynamical character during phase transition between Bardeen-Cooper-Schrieffer superfluid and topological superfluid. Our theoretical results display four kinds of single-particle excitations induced by the two-branch structure of single-particle spectrum, and the cross single-particle excitation is much easier to be seen in the spin dynamic structure factor at a small transferred momentum. Also we find a new roton-like collective mode emerges at a fixed transferred momentum $q \simeq 2k_F$, and it only appears once the system enters the topological superfluid state. The occurrence of this roton-like excitation is related to switch of global minimum in single-particle spectrum from $k=0$ to $k \simeq 2k_F$.