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Vortices in p-Wave Superfluids of Trapped Fermionic Atom Gases  [PDF]
Y. Tsutsumi,K. Machida
Physics , 2009, DOI: 10.1143/JPSJ.78.084702
Abstract: In order to help detecting superfluidity, we theoretically investigate p-wave pairing superfluids in neutral Fermion atom gases confined by a three dimensimentional (3D) harmonic potential. The Ginzburg-Landau framework, which is generic for p-wave superfluids, is used to describe the order parameter spatial structure, or texture characterized by the l-vector both at rest and under rotation. The l-vector configuration is strongly contrained by the boundary condition due to a trap. It is found that the ground state textures exhibit spontaneous supercurrent at rest both cigar and pancake shape traps. The current direction depends on the trapping shape. Under rotation a pair of half-quantum vortex with half-winding number enters a system and is stabilized for both trap geometries. We give detailed explanation for their 3D structure. The deformations of the condensate shape are seen with increasing the rotation speed, which is tightly connected with the underlying vortex formation where the condensates are depressed in the vortex core.
Beyond Gross-Pitaevskii:local density vs. correlated basis approach for trapped bosons  [PDF]
A. Fabrocini,A. Polls
Physics , 1999, DOI: 10.1103/PhysRevA.60.2319
Abstract: We study the ground state of a system of Bose hard-spheres trapped in an isotropic harmonic potential to investigate the effect of the interatomic correlations and the accuracy of the Gross-Pitaevskii equation. We compare a local density approximation, based on the energy functional derived from the low density expansion of the energy of the uniform hard sphere gas, and a correlated wave function approach which explicitly introduces the correlations induced by the potential. Both higher order terms in the low density expansion, beyond Gross-Pitaevskii, and explicit dynamical correlations have effects of the order of percent when the number of trapped particles becomes similar to that attained in recent experiments.
Stability of the singular vortex and associated Majorana zero modes in trapped p-wave resonant superfluids of neutral cold atoms  [PDF]
Y. Tsutsumi,K. Machida
Physics , 2009, DOI: 10.1143/JPSJ.79.034301
Abstract: The stability conditions for the singular vortex which accompanies Majorana zero modes at the core are investigated for p-wave resonant superfluids of atomic Fermi gases. Within the Ginzburg-Landau framework we determine the stable conditions in the parameter space for the external rotation frequency and the harmonic trap frequency. There exists the narrow stable region in this parameter space for quasi-two-dimensional condensates. We also describe the detailed characterizations of the spatial structure of the order parameter in the chiral p-wave superfluids under rotation.
Spontaneous mass current and textures of p-wave superfluids of trapped Fermionic atom gases at rest and under rotation  [PDF]
Y. Tsutsumi,K. Machida
Physics , 2008, DOI: 10.1103/PhysRevA.80.035601
Abstract: It is found theoretically based on the Ginzburg-Landau framework that p-wave superfluids of neutral atom gases in three dimension harmonic traps exhibit spontaneous mass current at rest, whose direction depends on trap geometry. Under rotation various types of the order parameter textures are stabilized, including Mermin-Ho and Anderson-Toulouse-Chechetkin vortices. In a cigar shape trap spontaneous current flows longitudial to the rotation axis and thus perpendicular to the ordinary rotational current. These features, spontaneous mass current at rest and texture formation, can be used as diagnoses for p-wave superfluidity.
Hydrodynamics of compressible superfluids in confined geometries  [PDF]
Abdul N Malmi-Kakkada,Oriol T Valls,Chandan Dasgupta
Physics , 2014, DOI: 10.1088/0953-4075/47/5/055301
Abstract: We present a study of the hydrodynamics of compressible superfluids in confined geometries. We use a perturbative procedure in terms of the dimensionless expansion parameter $(v/v_s)^2$ where $v$ is the typical speed of the flow and $v_s$ the speed of sound. A zero value of this parameter corresponds to the incompressible limit. We apply the procedure to two specific problems: the case of a trapped superfluid with a gaussian profile of the local density, and that of a superfluid confined in a rotating obstructed cylinder. We find that the corrections due to finite compressibility which are, as expected, negligible for liquid He, are important but amenable to the perturbative treatment for typical ultracold atomic systems.
Quasiparticle scattering and local density of states in the d-density wave phase  [PDF]
Cristina Bena,Sudip Chakravarty,Jiangping Hu,Chetan Nayak
Physics , 2003, DOI: 10.1103/PhysRevB.69.134517
Abstract: We study the effects of single-impurity scattering on the local density of states in the high-$T_c$ cuprates. We compare the quasiparticle interference patterns in three different ordered states: d-wave superconductor (DSC), d-density wave (DDW), and coexisting DSC and DDW (DSC-DDW). In the coexisting state, at energies below the DSC gap, the patterns are almost identical to those in the pure DSC state with the same DSC gap. However, they are significantly different for energies greater than or equal to the DSC gap. This transition at an energy around the DSC gap can be used to test the nature of the superconducting state of the underdoped cuprates by scanning tunneling microscopy. Furthermore, we note that in the DDW state the effect of the coherence factors is stronger than in the DSC state. The new features arising due to DDW ordering are discussed.
Critical Temperature of a Trapped Interacting Bose Gas in the Local Density Approximation  [PDF]
Hualin Shi,Wei-Mou Zheng
Physics , 1996, DOI: 10.1103/PhysRevA.56.1046
Abstract: The Bose gas in an external potential is studied by means of the local density approximation. An analytical result is derived for the dependence of the critical temperature of Bose-Einstein condensation on the mutual interaction in a generic power-law potential.
Gradient corrections to the local density approximation for trapped superfluid Fermi gases  [PDF]
András Csordás. Orsolya Almásy,Péter Szépfalusy
Physics , 2010, DOI: 10.1103/PhysRevA.82.063609
Abstract: Two species superfluid Fermi gas is investigated on the BCS side up to the Feshbach resonance. Using the Greens's function technique gradient corrections are calculated to the generalized Thomas-Fermi theory including Cooper pairing. Their relative magnitude is found to be measured by the small parameter $(d/R_{TF})^4$, where $d$ is the oscillator length of the trap potential and $R_{TF}$ is the radial extension of the density $n$ in the Thomas-Fermi approximation. In particular at the Feshbach resonance the universal %constant $A_{TF}$ has the %correction in the center $A=A_{TF}+A_2(d/R_{TF})^4+\...$ corrections to the local density approximation are calculated and a universal prefactor $\kappa_W=7/27$ is derived for the von Weizs\"acker type correction $\kappa_W(\hbar^2/2m)(\nabla^2 n^{1/2}/n^{1/2})$.
Mean-field study of itinerant ferromagnetism in trapped ultracold Fermi gases: Beyond the local density approximation  [PDF]
H Dong,Hui Hu,Xia-Ji Liu,Peter D. Drummond
Physics , 2010, DOI: 10.1103/PhysRevA.82.013627
Abstract: We theoretically investigate the itinerant ferromagnetic transition of a spherically trapped ultracold Fermi gas with spin imbalance under strongly repulsive interatomic interactions. Our study is based on a self-consistent solution of the Hartree-Fock mean-field equations beyond the widely used local density approximation. We demonstrate that, while the local density approximation holds in the paramagnetic phase, after the ferromagnetic transition it leads to a quantitative discrepancy in various thermodynamic quantities even with large atom numbers. We determine the position of the phase transition by monitoring the shape change of the free energy curve with increasing the polarization at various interaction strengths.
Self-Trapped Exciton Defects in a Charge Density Wave: Electronic Excitations of BaBiO3  [PDF]
Philip B. Allen,Ilka B. Bischofs
Physics , 2001, DOI: 10.1103/PhysRevB.65.115113
Abstract: In the previous paper, it was shown that holes doped into BaBiO3 self-trap as small polarons and bipolarons. These point defects are energetically favorable partly because they undo locally the strain in the charge-density-wave (Peierls insulator) ground state. In this paper the neutral excitations of the same model are discussed. The lowest electronic excitation is predicted to be a self-trapped exciton, consisting of an electron and a hole located on adjacent Bi atoms. This excitation has been seen experimentally (but not identified as such) via the Urbach tail in optical absorption, and the multi-phonon spectrum of the ``breathing mode'' seen in Raman scattering. These two phenomena occur because of the Franck-Condon effect associated with oxygen displacement in the excited state.
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