2,086 research outputs found
Landau levels and the Thomas-Fermi structure of rapidly rotating Bose-Einstein condensates
We show that, within mean-field theory, the density profile of a rapidly
rotating harmonically trapped Bose-Einstein condensate is of the Thomas-Fermi
form as long as the number of vortices is much larger than unity. Two forms of
the condensate wave function are explored: i) the lowest Landau level (LLL)
wave function with a regular lattice of vortices multiplied by a slowly varying
envelope function, which gives rise to components in higher Landau levels; ii)
the LLL wave function with a nonuniform vortex lattice. From variational
calculations we find it most favorable energetically to retain the LLL form of
the wave function but to allow the vortices to deviate slightly from a regular
lattice. The predicted distortions of the lattice are small, but in accord with
recent measurements at lower rates of rotation.Comment: 4 pages, 2 figures, to appear in Phys. Rev. Lett. (extend the
arguments of cond-mat/0402167
Bose-Einstein condensate in a rapidly rotating non-symmetric trap
A rapidly rotating Bose-Einstein condensate in a symmetric two-dimensional
harmonic trap can be described with the lowest Landau-level set of
single-particle states. The condensate wave function psi(x,y) is a Gaussian
exp(-r^2/2), multiplied by an analytic function f(z) of the complex variable z=
x+ i y. The criterion for a quantum phase transition to a non-superfluid
correlated many-body state is usually expressed in terms of the ratio of the
number of particles to the number of vortices. Here, a similar description
applies to a rapidly rotating non-symmetric two-dimensional trap with arbitrary
quadratic anisotropy (omega_x^2 < omega_y^2). The corresponding condensate wave
function psi(x,y) is a complex anisotropic Gaussian with a phase proportional
to xy, multiplied by an analytic function f(z), where z = x + i \beta_- y is a
stretched complex variable and 0< \beta_- <1 is a real parameter that depends
on the trap anisotropy and the rotation frequency. Both in the mean-field
Thomas-Fermi approximation and in the mean-field lowest Landau level
approximation with many visible vortices, an anisotropic parabolic density
profile minimizes the energy. An elongated condensate grows along the soft trap
direction yet ultimately shrinks along the tight trap direction. The criterion
for the quantum phase transition to a correlated state is generalized (1) in
terms of N/L_z, which suggests that a non-symmetric trap should make it easier
to observe this transition or (2) in terms of a "fragmented" correlated state,
which suggests that a non-symmetric trap should make it harder to observe this
transition. An alternative scenario involves a crossover to a quasi
one-dimensional condensate without visible vortices, as suggested by Aftalion
et al., Phys. Rev. A 79, 011603(R) (2009).Comment: 20 page
Mechanism of d_{x^2-y^2}-wave superconductivity based on doped hole induced spin texture in high T_c cuprates
A mechanism of d_{x^2-y^2}-wave superconductivity is proposed for the
high-T_c cuprates based on a spin texture with non-zero topological density
induced by doped holes through Zhang-Rice singlet formation. The pairing
interaction arises from the magnetic Lorentz force like interaction between the
holes and the spin textures. The stability of the pairing state against the
vortex-vortex interaction and the Coulomb repulsion is examined. The mechanism
suggests appearance of a p-wave pairing component by introducing anisotropy in
the CuO_2 plane.Comment: 9 pages, 3 figures; added references, corrected minor error
Effective bosonic hamiltonian for excitons : a too naive concept
Excitons, being made of two fermions, may appear from far as bosons. Their
close-to-boson character is however quite tricky to handle properly. Using our
commutation technique especially designed to deal with interacting
close-to-boson particles, we here calculate the exact expansion in Coulomb
interaction of theexciton-exciton correlations, and show that a naive effective
bosonic hamiltonian for excitons cannot produce these X-X correlations
correctly
An effective theory of Feshbach resonances and many-body properties of Fermi gases
For calculating low-energy properties of a dilute gas of atoms interacting
via a Feshbach resonance, we develop an effective theory in which the
parameters that enter are an atom-molecule coupling strength and the magnetic
moment of the molecular resonance. We demonstrate that for resonances in the
fermionic systems Li and K that are under experimental
investigation, the coupling is so strong that many-body effects are appreciable
even when the resonance lies at an energy large compared with the Fermi energy.
We calculate a number of many-body effects, including the effective mass and
the lifetime of atomic quasiparticles in the gas.Comment: 4 pages, 1 figure, NORDITA-2003-21 C
Medical applications of nasa-developed science and technology quarterly progress report no. 2, 30 apr. - 31 jul. 1965
Medical applications of aerospace science and technolog
Normal Modes of a Vortex in a Trapped Bose-Einstein Condensate
A hydrodynamic description is used to study the normal modes of a vortex in a
zero-temperature Bose-Einstein condensate. In the Thomas-Fermi (TF) limit, the
circulating superfluid velocity far from the vortex core provides a small
perturbation that splits the originally degenerate normal modes of a
vortex-free condensate. The relative frequency shifts are small in all cases
considered (they vanish for the lowest dipole mode with |m|=1), suggesting that
the vortex is stable. The Bogoliubov equations serve to verify the existence of
helical waves, similar to those of a vortex line in an unbounded weakly
interacting Bose gas. In the large-condensate (small-core) limit, the
condensate wave function reduces to that of a straight vortex in an unbounded
condensate; the corresponding Bogoliubov equations have no bound-state
solutions that are uniform along the symmetry axis and decay exponentially far
from the vortex core.Comment: 15 pages, REVTEX, 2 Postscript figures, to appear in Phys. Rev. A. We
have altered the material in Secs. 3B and 4 in connection with the normal
modes that have |m|=1. Our present treatment satisfies the condition that the
fundamental dipole mode of a condensate with (or without) a vortex should
have the bare frequency $\omega_\perp
Beyond the Thomas-Fermi approximation for a trapped condensed Bose-Einstein gas
Corrections to the zero-temperature Thomas-Fermi description of a dilute
interacting condensed Bose-Einstein gas confined in an isotropic harmonic trap
arise due to the presence of a boundary layer near the condensate surface.
Within the Bogoliubov approximation, the various contributions to the
ground-state condensate energy all have terms of order R^{-4}ln R and R^{-4},
where R is the number-dependent dimensionless condensate radius in units of the
oscillator length. The zero-order hydrodynamic density-fluctuation amplitudes
are extended beyond the Thomas-Fermi radius through the boundary layer to
provide a uniform description throughout all space. The first-order correction
to the excitation frequencies is shown to be of order R^{-4}.Comment: 12 pages, 2 figures, revtex. Completely revised discussion of the
boundary-layer corrections to collective excitations, and two new figures
added. To appear in Phys. Rev. A (October, 1998
An Active-Sterile Neutrino Transformation Solution for r-Process Nucleosynthesis
We discuss how matter-enhanced active-sterile neutrino transformation in both
neutrino and antineutrino channels could enable the production of the rapid
neutron capture (r-process) nuclei in neutrino-heated supernova ejecta. In this
scheme the lightest sterile neutrino would be heavier than the electron
neutrino and split from it by a vacuum mass-squared difference roughly between
3 and 70 eV and vacuum mixing angle given by .Comment: 27 pages plus twelve figures. Submitted to Phys. Rev.
Many-Body Theory of the Electroweak Nuclear Response
After a brief review of the theoretical description of nuclei based on
nonrelativistic many-body theory and realistic hamiltonians, these lectures
focus on its application to the analysis of the electroweak response. Special
emphasis is given to electron-nucleus scattering, whose experimental study has
provided a wealth of information on nuclear structure and dynamics, exposing
the limitations of the shell model. The extension of the formalism to the case
of neutrino-nucleus interactions, whose quantitative understanding is required
to reduce the systematic uncertainty of neutrino oscillation experiments, is
also discussed.Comment: Lectures delivered at the DAE-BRNS Workshop on Hadron Physics.
Aligarh Muslim University, Aligarh (India), February 18-23, 200
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