31 research outputs found
Topological Vortex Formation in BEC under Gravitational Field
Topological phase imprinting is a unique technique for vortex formation in a
Bose-Einstein condensate (BEC) of alkali metal gas, in that it does not involve
rotation: BEC is trapped in a quadrupole field with a uniform bias field which
is reversed adiabatically leading to vortex formation at the center of the
magnetic trap. The scenario has been experimentally verified by MIT group
employing Na atoms. Recently similar experiments have been conducted at
Kyoto University, in which BEC of Rb atoms has been used. In the latter
experiments they found that the fine-tuning of the field reverse time is required to achieve stable vortex formation. Otherwise, they often
observed vortex fragmentations or a condensate without a vortex. It is shown in
this paper that this behavior is attributed to the heavy mass of the Rb atom.
The confining potential, which depends on the eigenvalue of the hyperfine
spin \bv{F} along the magnetic field, is now shifted by the gravitational
field perpendicular to the vortex line. Then the positions of two
weak-field-seeking states with and 2 deviate from each other. This
effect is more prominent for BEC with a heavy atomic mass, for which the
deviation is greater and, moreover, the Thomas-Fermi radius is smaller. We
found, by solving the Gross-Pitaevskii equation numerically, that two
condensates interact in a very complicated way leading to fragmentation of
vortices, unless is properly tuned.Comment: 7 pages, 3 figures submitted to PR
Orbital symmetry of a triplet pairing in a heavy Fermion superconductor UPt_3
The orbital symmetry of the superconducting order parameter in UPt_3 is
identified by evaluating the directionally dependent thermalconductivity and
ultrasound attenuation in the clean limit and compared with the existing data
for both basal plane and the c-axis of a hexagonal crystal. The resulting two
component orbital part expressed by (\lambda_x(k), \lambda_y(k)) is combined
with the previously determined triplet spin part, leading to clean limit and
compared with the existing data for both basal plane and the c-axis of a
hexagonal crystal. The resulting two component orbital part expressed by
(\lambda_x(k), \lambda_y(k)) is combined with the previously determined triplet
spin part, leading to the order parameter of either the non-unitary bipolar
state of the form: d(k) = b \lambda_x(k) + i j \lambda_y(k) or the unitary
planar state of the form: d(k) = b \lambda_x(k) + j \lambda_y(k) where b \perp
j = c, or a with the hexagonal unit vectors a, b and c. The d vector is
rotatable in the plane spanned by a and c perpendicular to b under weak applied
c-axis field because of the weak spin orbit coupling. Experiments are proposed
to distinguish between the equally possible these states.Comment: 8 pages, 8 eps figure
A simple method to create a vortex in Bose-Einstein condensate of alkali atoms
Bose-Einstein condensation in alkali atoms has materialized quite an
interesting system, namely a condensate with a spin degree of freedom. In
analogy with the A-phase of the superfluid He, numerous textures with
nonvanishing vorticity have been proposed. In the present paper, interesting
properties of such spin textures are analyzed. We propose a remarkably simple
method to create a vortex state of a BEC in alkali atoms.Comment: 2 pages, 1 eps figure. Proceedings of LT22. The title is changed from
the submitted version: Vortices in Bose-Einstein condensate with spin degree
of freedo