Normal density and moment of inertia of a moving superfluid

Abstract

In this work, the normal density ρn and moment of inertia of a moving superfluid are investigated. We find that, even at zero temperature, there exists a finite normal density for the moving superfluid. When the velocity of superfluid reaches sound velocity, the normal density becomes total mass density ρ, which indicates that the system losses superfluidity. At the same time, the Landau’s critical velocity also becomes zero. The existence of the non-zero normal density is attributed to the coupling between the motion of superflow and density fluctuation in transverse directions. With Josephson relation, the superfluid density ρs is also calculated and the identity ρs + ρn = ρ holds. Further more, we find that the finite normal density also results in a quantized moment of inertia in a moving superfluid trapped by a ring. The normal density and moment of inertia at zero temperature could be verified experimentally by measuring the angular momentum of a moving superfluid in a ring trap.

Superfluid fraction tensor of a two-dimensional supersolid

“…A future direction would be to consider the extension of these ideas to superfluidity of the stripe phase of a spin-orbit coupled BEC (see [52][53][54][55]), in which Galilean invariance is also broken. It might also be necessary to explore scenarios in which the supersolid state may not necessarily be the ground state, but rather exhibits specific excitations of its phase profile [56] (also see [57]) or lattice distortions. In the latter case, our results already suggest this will lead to anisotropic effects in the superfluid response.…”

Superfluid density, Josephson relation and pairing fluctuations in a multi-component fermion superfluid

“…In addition, it is found that, there exist only one gapless excitation near q = 0, which corresponds to total density oscillations. The superfluid density can be also calculated with current-current correlation [10,32,48] or phase twist method [49,50]. Assuming the superfluid order parameters undergo a phase variation, e.g, △ i → ∆ i e 2iq•ri , The superfluid density (particle number per unit cell) tensor ρ sij can be written as…”

Superfluid density, Josephson relation and pairing fluctuations in a multi-component fermion superfluid

“…In addition, it is found that, there exists only one gapless excitation near , which corresponds to total density oscillations. The superfluid density can be also calculated with current–current correlation functions 9 , 34 , 47 or phase twist method 46 , 60 . Assuming the superfluid order parameters undergo a phase variation, e.g, , the superfluid density (particle number per unit cell) tensor can be written as where is thermodynamical potential (per unit cell) in grand canonical ensemble.…”