Anomalous dispersion of the collective modes of an ultracold $^6Li-$ $^{40}K$ mixture in a square optical lattice

TL;DR

This paper predicts that in a superfluid mixture of imbalanced Lithium-6 and Potassium-40 atoms in a square optical lattice, the collective modes can exhibit anomalous dispersion, which could be observed under specific conditions.

Contribution

It provides numerical predictions of collective excitation spectra and identifies conditions for anomalous dispersion in an ultracold Fermi-Fermi mixture in a lattice.

Findings

Anomalous dispersion of collective modes predicted in the Fulde-Ferrell phase.

Dispersion initially bends upward before bending over with increasing quasimomentum.

Conditions depend on polarization, interaction strength, and temperature.

Abstract

We report numerical calculations of the collective excitation spectrum and the speed of sound of the superfluid phase of an atomic Fermi-Fermi mixture of population-imbalanced Lithium-6 and Potassium-40 atoms in a square lattice. It is predicted that in the exotic states of matter, known as the Fulde-Ferrell phase, an anomalous dispersion of the collective modes may be realized at some values of polarization, interacting strength and temperature, i.e. the collective-mode dispersion initially bends upward before bending over as the quasimomentum increases.