Collective Excitations in Bose–Fermi Mixtures

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 a 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.

Dipole oscillation of a trapped Bose-Fermi-mixture gas in collisionless and hydrodynamic regimes

“…These distinct quantum statistical properties may give rise to an interesting feature of collective modes. The earlier study showed that there surprisingly exists a long-lived sound mode between the hydrodynamic regime and the collisionless regime [23]; this is in contrast to our general knowledge, where a lifetime of the collective mode is very short in the crossover regime.…”

“…In an earlier study [23], we examined a collective sound mode in a normal phase of a uniform Bose-Fermi mixture, composed of single-species bosons and single-species fermions interacting via s-wave scatterings, where collisions between fermions are absent because of the Pauliblocking. The intraspecies (Bose-Bose) scattering becomes important at low temperature close to the BEC transition temperature because of Bose-enhancement, which may lead to the hydrodynamic regime.…”

Dipole Mode of Trapped Bose–Fermi Mixture Gas

“…These competitive quantum statistical properties may give rise to an interesting property of collective modes. In fact, in the case of a spatial uniform system, there exists a long-lived sound mode in the crossover region between collisionless and hydrodynamic regimes [10]. In this paper, considering the familiar experimental situation in ultracold atomic gases, we study dipole modes in a Bose-Fermi mixture for exploring exotic collective mode.…”