# Leggett mode in a two-component Fermi gas with dipolar interactions

## TL;DR

This paper develops an effective field theory to analyze collective excitations, including a Leggett mode, in a three-dimensional two-component dipolar Fermi superfluid, revealing conditions for its existence and potential experimental detection.

## Contribution

It introduces a theoretical framework for understanding the Leggett mode in dipolar Fermi gases, highlighting the conditions for its emergence and how it can be observed.

## Key findings

- Existence of an undamped massive Leggett mode in certain interaction regimes.
- The Leggett mode appears in the spectral function of Cooper pairs.
- Potential detection of the Leggett mode via Bragg spectroscopy.

## Abstract

We develop an effective field theory to understand collective modes of a three-dimensional two-component Fermi superfluid with dipolar inter-particle interactions, which are modeled by an idealized separable potential. We first examine the phase transition of the system at zero temperature, as the fermionic superfluidity is known to be characterized by two competing order parameters. We find that for strong interactions there exists a regime where the two order parameters are out-of-phase and coupled, giving rise to an undamped massive Leggett mode. This is in addition to the well-known gapless phonon mode. We show that the Leggett mode can be seen in the spectral function of the in-medium Cooper pairs, and in principle could be measured through Bragg spectroscopy.