Critical angular velocities for two-dimensional superfluidity

Francesco Piazza, Lee A. Collins, Augusto Smerzi

Biao Wu, Junren Shi

L. Yu. Kravchenko, D. V. Fil

Miodrag L. Kulić, Armen Sedrakian, Dirk H. Rischke

A rotating ultracold $S$-wave superfluid Fermi gas is studied when the mismatch in chemical potentials $\ensuremath{\delta}\ensuremath{\mu}$ (and the population imbalance $\ensuremath{\delta}n$) corresponds to the Larkin-Ovchinnikov-Fulde-Ferrell state in the vicinity of the Lifshitz critical point. It is shown that under these conditions the critical angular velocity ${\ensuremath{\Omega}}_{c2}$ in two-dimensional systems is an oscillating function of temperature and $\ensuremath{\delta}n$ giving rise to reentrant superfluid phases. The reason for this behavior is the population by Cooper pairs of the Landau levels $(n\ensuremath{\ge}1)$ above the lowest one $(n=0)$.

David M. F. Chapman

The equations of motion of vortices in an ideal two-dimensional fluid are derived, and the laws of conservation associated with the motion are discussed. Two regions of flow are considered, an infinite region and a region bounded on the outside by a circle. The kinetic energy and angular momentum of a vortex fluid in these two regions are calculated. A Lagrangian formalism is introduced in order to discuss the symmetry transformations of vortex systems and their associated conservation laws. The kinematic stability of rigidly rotating polygonal configurations of quantized vortices is determined, and the states of thermodynamic equilibrium of a rotating superfluid are found for low angular velocities, resulting in the calculation of the spectrum of critical angular velocities for the creation of one, two, and three vortices.

I. Bausmerth, Alessio Recati, S. Stringari

We study the effect of the rotation on a harmonically trapped Fermi gas at zero temperature under the assumption that vortices are not formed. We show that at unitarity the rotation produces a phase separation between a nonrotating superfluid (S) core and a rigidly rotating normal (N) gas. The interface between the two phases is characterized by a density discontinuity n(N)/n(S)=0.85, independent of the angular velocity. The depletion of the superfluid and the angular momentum of the rotating configuration are calculated as a function of the angular velocity. The conditions of stability are also discussed and the critical angular velocity for the onset of a spontaneous quadrupole deformation of the interface is evaluated.