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

Abstract

We develop an effective field theory to understand collective modes of a three-dimensional twocomponent 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 wellknown 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.

Dispersion and Damping of Phononic Excitations in Fermi Superfluid Gases in 2D

“…In the opposite case of a relatively small-radius confinement potential, the hydrodynamic approach used in Reference [20] can effectively determine spectra of discrete low-lying modes. Another promising development of the present study is related to the collective modes in ultra-cold Fermi gases with dipolar interactions intensely investigated recently [30][31][32]. Different interaction potentials, as well as a deformation of the Fermi surface [32] can be straightforwardly incorporated in the GPF approach.…”

Stability of quantum degenerate Fermi gases of tilted polar molecules

“…A recent experiment [22,23] measured that for a fermionic gas of magnetic dipolar erbium atoms an ellipsoidal deformation of the Fermi sphere occurs, which is of the order of 2%. This is expected to lead to novel many-body phenomena, in particular in connection with fermionic superfluidity [24][25][26][27][28][29]. In a polarized onecomponent Fermi gas an intriguing interplay between an anisotropic order parameter with odd partial waves and the FS deformation enhances superfluid pairing via mod-ifying the density of states [26].…”