Collective excitations in Bose-Fermi mixtures

TL;DR

This paper studies how collective excitations in Bose-Fermi mixtures behave across temperatures, revealing deviations from hydrodynamic and collisionless limits due to boson-fermion collisions.

Contribution

It provides new insights into the temperature-dependent behavior of collective modes in Bose-Fermi mixtures, highlighting the impact of boson-fermion collisions.

Findings

Collective mode frequency deviates from hydrodynamic sound at lower temperatures.

Even at low temperatures, the mode does not reach the collisionless zero sound limit.

Boson-fermion collisions significantly influence collective excitations.

Abstract

We investigate collective excitations of density fluctuations and a dynamic density structure factor in a mixture of Bose and Fermi gases in a normal phase. With decreasing temperature, we find that the frequency of the collective excitation deviates from that of the hydrodynamic sound mode. Even at temperature much lower than the Fermi temperature, the collective mode frequency does not reach the collisionless limit analogous to zero sound in a Fermi gas, because of collisions between bosons and fermions.