Dynamic structure factors of a strongly interacting Fermi superfluid near an orbital Feshbach resonance across the phase transition from BCS to Sarma superfluid

TL;DR

This paper theoretically analyzes the dynamic structure factors of a strongly interacting Fermi superfluid near an orbital Feshbach resonance, revealing how these factors change across the BCS to Sarma superfluid phase transition and providing ways to distinguish different superfluid states.

Contribution

It introduces a theoretical framework using the random phase approximation to study the dynamic structure factors during the BCS to Sarma superfluid transition, highlighting unique excitations in the Sarma phase.

Findings

Dynamic structure factors distinguish BCS and Sarma superfluids via excitation modes.

Sarma superfluid exhibits gapless excitations and strong atomic signals at large momentum.

The study provides criteria to identify superfluid phases based on excitation spectra.

Abstract

We theoretically investigate dynamic structure factors of a strongly interacting Fermi superfluid near an orbital Feshbach resonance with random phase approximation, and find their dynamical characters during the phase transition between a balanced conventional Bardeen-Cooper-Schrieffer superfluid and a polarized Sarma superfluid by continuously varying the chemical potential difference of two spin components. In a BEC-like regime of the BCS superfluid, dynamic structure factors can do help to distinguish the in-phase ground state from the out-of-phase metastable state by the relative location of molecular excitation and Leggett mode, or the minimum energy to break a Cooper pair. In the phase transition between BCS and Sarma superfluid, we find the dynamic structure factor of Sarma superfluid has its own specific gapless excitation at a small transferred momentum which is mixed with the collective phonon excitation, and also a relatively strong atomic excitation at a large transferred momentum because of the existence of unpaired Fermi atoms, these signals can be used to differentiate Sarma superfluid from BCS superfluid.