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Phase diagram of the rotating two-component Fermi gas including vortices  [PDF]
Harmen J. Warringa
Physics , 2012,
Abstract: We determine the conditions under which superfluidity with and without quantized vortices appears in a weakly interacting two-component atomic Fermi gas that is trapped in a rotating cylindrical symmetric harmonic potential. We compute the phase diagram as a function of rotation frequency, scattering length, temperature, total number of trapped atoms, and population imbalance.
Phase diagram of quantized vortices in a trapped Bose-Einstein condensed gas  [PDF]
S. Stringari
Physics , 1998, DOI: 10.1103/PhysRevLett.82.4371
Abstract: We investigate the thermodynamic stability of quantized vortices in a dilute Bose gas confined by a rotating harmonic trap at finite temperature. Interatomic forces play a crucial role in characterizing the resulting phase diagram, especially in the large $N$ Thomas-Fermi regime. We show that the critical temperature for the creation of stable vortices exhibits a maximum as a function of the frequency of the rotating trap and that the corresponding transition is associated with a discontinuity in the number of atoms in the condensate. Possible strategies for approaching the vortical region are discussed.
Multiple-quantized vortices in rotating LOFF state of ultracold Fermi superfluid gas  [PDF]
Miodrag L. Kulic,Armen Sedrakian,Dirk H. Rischke
Physics , 2009, DOI: 10.1103/PhysRevA.80.043610
Abstract: A rotating ultracold S-wave superfluid Fermi gas is considered, when the population imbalance (or equivalently the mismatch in chemical potentials) corresponds to the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state in the vicinity of the Lifshitz critical point. It is shown that under these conditions the critical angular velocity in two-dimensional systems is an oscillating function of temperature and population imbalance giving rise to reentrant superfluid phases. This leads to vortex lattices with multiple-quantized circulation quanta. The reason for this behavior is the population by Cooper pairs of the Landau levels above the lowest one.
Destroying superfluidity by rotating a Fermi gas at unitarity  [PDF]
I. Bausmerth,A. Recati,S. Stringari
Physics , 2007, DOI: 10.1103/PhysRevLett.100.070401
Abstract: 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 non rotating superfluid (S) core and a rigidly rotating normal (N) gas. The interface between the two phases is characterized by a density discontinuity $n_{\rm N}/n_{\rm S}= 0.85$, 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.
Vortices and Superfluidity in a Strongly Interacting Fermi Gas  [PDF]
M. W. Zwierlein,J. R. Abo-Shaeer,A. Schirotzek,C. H. Schunck,W. Ketterle
Physics , 2005, DOI: 10.1038/nature03858
Abstract: Quantum-degenerate Fermi gases provide a remarkable opportunity to study strongly interacting fermions. In contrast to other Fermi systems, such as superconductors, neutron stars or the quark-gluon plasma, these gases have low densities and their interactions can be precisely controlled over an enormous range. Here we report observations of vortices in such a gas that provide definitive evidence for superfluidity. By varying the pairing strength between two fermions near a Feshbach resonance, one can explore the crossover from a Bose-Einstein condensate (BEC) of molecules to a Bardeen-Cooper-Schrieffer (BCS) superfluid of loosely bound pairs whose size is comparable to, or even larger than, the interparticle spacing. The crossover realizes a novel form of high-T_C superfluidity and it may provide new insight for high-T_C superconductors. Previous experiments with Fermi gases have revealed condensation of fermion pairs. While these and other studies were consistent with predictions assuming superfluidity, the smoking gun for superfluid behavior has been elusive. Our observation of vortex lattices directly displays superfluid flow in a strongly interacting, rotating Fermi gas.
Vortex formation in a rotating two-component Fermi gas  [PDF]
Harmen J. Warringa,Armen Sedrakian
Physics , 2011, DOI: 10.1103/PhysRevA.84.023609
Abstract: A two-component Fermi gas with attractive s-wave interactions forms a superfluid at low temperatures. When this gas is confined in a rotating trap, fermions can unpair at the edges of the gas and vortices can arise beyond certain critical rotation frequencies. We compute these critical rotation frequencies and construct the phase diagram in the plane of scattering length and rotation frequency for different total number of particles. We work at zero temperature and consider a cylindrically symmetric harmonic trapping potential. The calculations are performed in the Hartree-Fock-Bogoliubov approximation which implies that our results are quantitatively reliable for weak interactions.
Formation of a vortex lattice in a rotating BCS Fermi gas  [PDF]
Giulia Tonini,Félix Werner,Yvan Castin
Physics , 2005, DOI: 10.1140/epjd/e2006-00110-7
Abstract: We investigate theoretically the formation of a vortex lattice in a superfluid two-spin component Fermi gas in a rotating harmonic trap, in a BCS-type regime of condensed non-bosonic pairs. Our analytical solution of the superfluid hydrodynamic equations, both for the 2D BCS equation of state and for the 3D unitary quantum gas, predicts that the vortex free gas is subject to a dynamic instability for fast enough rotation. With a numerical solution of the full time dependent BCS equations in a 2D model, we confirm the existence of this dynamic instability and we show that it leads to the formation of a regular pattern of quantum vortices in the gas.
Rotating a Rashba-coupled Fermi gas in two dimensions  [PDF]
E. Doko,A. L. Subasi,M. Iskin
Physics , 2015,
Abstract: We analyze the interplay of adiabatic rotation and Rashba spin-orbit coupling on the BCS-BEC evolution of a harmonically-trapped Fermi gas in two dimensions, under the assumption that vortices are not excited. First, by taking the trapping potential into account via both the semi-classical and exact quantum-mechanical approaches, we firmly establish the parameter regime where the non-interacting gas forms a ring-shaped annulus. Then, by taking the interactions into account via the BCS mean-field approximation, we study the pair-breaking mechanism that is induced by rotation, \textit{i.e.}, the Coriolis effects. In particular, we show that the interplay allows for the possibility of creating either an isolated annulus of rigidly-rotating normal particles that is disconnected from the central core of non-rotating superfluid pairs or an intermediate mediator phase where the superfluid pairs and normal particles coexist as a partially-rotating gapless superfluid.
Vortex arrays in a rotating superfluid Fermi gas  [PDF]
David L. Feder
Physics , 2004, DOI: 10.1103/PhysRevLett.93.200406
Abstract: The behavior of a dilute two-component superfluid Fermi gas subjected to rotation is investigated within the context of a weak-coupling BCS theory. The microscopic properties at finite temperature are obtained by iterating the Bogoliubov-de Gennes equations to self-consistency. In the model, alkali atoms are strongly confined in quasi-two-dimensional traps produced by a deep one-dimensional optical lattice. The lattice depth significantly enhances the critical transition temperature and the critical rotation frequency at which the superfluidity ceases. As the rotation frequency increases, the triangular vortex arrays become increasingly irregular, indicating a quantum melting transition.
Superfluid Expansion of a Strongly Interacting Fermi Gas  [PDF]
C. H. Schunck,M. W. Zwierlein,A. Schirotzek,W. Ketterle
Physics , 2006, DOI: 10.1103/PhysRevLett.98.050404
Abstract: We study the expansion of a rotating, superfluid Fermi gas. The presence and absence of vortices in the rotating gas is used to distinguish superfluid and normal parts of the expanding cloud. We find that the superfluid pairs survive during the expansion until the density decreases below a critical value. Our observation of superfluid flow at this point extends the range where fermionic superfluidity has been studied to densities of 1.2 10^{11} cm^{-3}, about an order of magnitude lower than any previous study.
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