Zero Sound in Fermi Dipolar Condensates

Paulsamy Muruganandam, Sadhan K. Adhikari

Boris Luk’yanchuk, D. M. Semiz

Shohei Watabe, Aiko Osawa, Tetsuro Nikuni

A.M. Badalyan, Leonid A. Maksimov

Shai Ronen, John L. Bohn

We study the propagation of sound in a homogeneous dipolar gas at zero temperature, which is known as zero sound. We find that undamped zero sound propagation is possible only in a range of solid angles around the direction of polarization of the dipoles. Above a critical dipole moment, we find an unstable mode, by which the gas collapses locally perpendicular to the dipoles' direction.

Takahiko Miyakawa, Eiji Nakano, Hiroyuki Yabu

We investigate collective excitations in a dipolar and non-dipolar Fermi gas mixture at zero temperature.We obtain the density-density correlation functions of the mixtures in the ring diagram approximation.We analyze the dispersion relation determined by the poles of the density-density correlation functions and find two different types of collective modes: the undamped zero sound and the overdamped modes.We show that the undamped zero sound mode exists only at long wavelengths and the speed of undamped zero sound varies with the propagation direction due to an anisotropy of the dipolar interaction between dipolar fermions.We also show that the decay rate of the overdamped mode decreases as the inter-particle interaction strength between dipolar and non-dipolar fermions increases and the overdamped mode is replaced by unstable one if the inter-particle interaction strength is much strong.