The low-temperature dependence of quasiparticle sound velocity in a nonideal Bose gas is investigated. Besides a ${T}^{4}$ ln ${T}^{\ensuremath{-}1}$ increase with temperature - formally identical to that obtained by Khalatnikov and Andreyev for He II by the kinetic-equation approach - a ${T}^{4}$ decrease of the sound velocity is found. Assuming the theoretical expressions to remain formally valid for superfluid helium, comparison is made with experimental results on the variation of sound velocity with temperature.The low-temperature dependence of quasiparticle sound velocity in a nonideal Bose gas is investigated. Besides a ${T}^{4}$ ln ${T}^{\ensuremath{-}1}$ increase with temperature - formally identical to that obtained by Khalatnikov and Andreyev for He II by the kinetic-equation approach - a ${T}^{4}$ decrease of the sound velocity is found. Assuming the theoretical expressions to remain formally valid for superfluid helium, comparison is made with experimental results on the variation of sound velocity with temperature.

Physical review. B, Condensed matterFeb 1, 197812 citations

The universal sound velocity formula for the strongly interacting unitary Fermi gas

Ke Liu, Jisheng Chen

Due to the scale invariance, the thermodynamic laws of strongly interacting limit unitary Fermi gas can be similar to those of non-interacting ideal gas. For example, the virial theorem between pressure and energy density of the ideal gas P = 2 E /3 V is still satisfied by the unitary Fermi gas. This paper analyses the sound velocity of unitary Fermi gases with the quasi-linear approximation. For comparison, the sound velocities for the ideal Boltzmann, Bose and Fermi gas are also given. Quite interestingly, the sound velocity formula for the ideal non-interacting gas is found to be satisfied by the unitary Fermi gas in different temperature regions.Due to the scale invariance, the thermodynamic laws of strongly interacting limit unitary Fermi gas can be similar to those of non-interacting ideal gas. For example, the virial theorem between pressure and energy density of the ideal gas P = 2 E /3 V is still satisfied by the unitary Fermi gas. This paper analyses the sound velocity of unitary Fermi gases with the quasi-linear approximation. For comparison, the sound velocities for the ideal Boltzmann, Bose and Fermi gas are also given. Quite interestingly, the sound velocity formula for the ideal non-interacting gas is found to be satisfied by the unitary Fermi gas in different temperature regions.

Chinese Physics BFeb 1, 20115 citations

Collisionless sound in a uniform two-dimensional Bose gas

M Ota, F Larcher, F Dalfovo +3 more

Oct 5, 20180 citations

Single-particle spectral density of a Bose gas in the two-fluid hydrodynamic regime

Emiko Arahata, Tetsuro Nikuni, Allan Griffin

In Bose superfluids, the single-particle Green's function can be directly related to the superfluid velocity-velocity correlation function in the hydrodynamic regime. An explicit expression for the single-particle spectral density was originally written down by Hohenberg and Martin in 1965, starting from the two-fluid equations for a superfluid. We give a simple derivation of their results. Using these results, we calculate the relative weights of first and second sound modes in the single-particle spectral density as a function of temperature in a uniform Bose gas. We show that the second sound mode makes a dominant contribution to the single-particle spectrum in a relatively high-temperature region. We also discuss the possibility of experimental observation of the second sound mode in a Bose gas by photoemission spectroscopy.In Bose superfluids, the single-particle Green's function can be directly related to the superfluid velocity-velocity correlation function in the hydrodynamic regime. An explicit expression for the single-particle spectral density was originally written down by Hohenberg and Martin in 1965, starting from the two-fluid equations for a superfluid. We give a simple derivation of their results. Using these results, we calculate the relative weights of first and second sound modes in the single-particle spectral density as a function of temperature in a uniform Bose gas. We show that the second sound mode makes a dominant contribution to the single-particle spectrum in a relatively high-temperature region. We also discuss the possibility of experimental observation of the second sound mode in a Bose gas by photoemission spectroscopy.

arXiv:1108.2382Physical Review ANov 14, 20115 citations

Excitations in bose-condensed gas

Shingo Otsuka

Jan 1, 20020 citations

The low-temperature dependence of quasiparticle sound velocity in a nonideal Bose gas is investigated. Besides a

{T}^{4}

ln ${T}^{\ensuremath{-}1}$ increase with temperature - formally identical to that obtained by Khalatnikov and Andreyev for He II by the kinetic-equation approach - a

{T}^{4}

decrease of the sound velocity is found. Assuming the theoretical expressions to remain formally valid for superfluid helium, comparison is made with experimental results on the variation of sound velocity with temperature.