58 research outputs found
Comment on "Ferromagnetic film on a superconducting substrate"
A superconducting substrate is not able to shrink drastically domains in a
ferromagnetic film, contrary to the prediction of Bulaevskii and Chudnovsky
[Phys. Rev. B, 63, issue1 (2001)]. This is shown on the basis of the exact
solution for the stripe domain structure.Comment: 8 pages, 1 figure, the version published in Phys. Rev.
Domain structure of superconducting ferromagnets
In superconducting ferromagnets the equilibrium domain structure is absent in
the Meissner state, but appears in the spontaneous vortex phase (the mixed
state in zero external magnetic field), though with a period, which can
essentially exceed that in normal ferromagnets. Metastable domain walls are
possible even in the Meissner state. The domain walls create magnetostatic
fields near the sample surface, which can be used for experimental detection of
domain walls.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Let
Iordanskii Force and the Gravitational Aharonov-Bohm effect for a Moving Vortex
I discuss the scattering of phonons by a vortex moving with respect to a
superfluid condensate. This allows us to test the compatibility of the
scattering-theory derivation of the Iordanskii force with the galilean
invariance of the underlying fluid dynamics. In order to obtain the correct
result we must retain terms in the sound-wave equation, and this
reinforces the interpretation, due to Volovik, of the Iordanskii force as an
analogue of the gravitational Bohm-Aharonov effect.Comment: 20 pages, LaTe
The electromagnetic response of a superconducting ferromagnets
The electromagnetic response of the superconducting ferromagnets RuSr₂Gd₁.₅Ce₀.₅Cu₂O₁₀ (Ru–1222
Gd) in an ac magnetic field of finite amplitude is investigated. Taking into account weak links between granules
and magnetization of the magnetic sublattice, it is shown that the response of a sample in a superconducting
state with the fundamental frequency and frequency of the 3rd harmonic can be described by the
nonlinear equation for the macroscopic field. Generation of the harmonic at temperatures above superconducting
transition corresponds to Rayleigh`s mechanism. Using various regimes of a sample cooling, the internal
magnetic field determined by the magnetic sublattice was measured. This is direct evidence of the coexistence
of ferromagnetic and superconductive order parameters in high-Tc ruthenocuprates
Dissipative dynamics of vortex arrays in anisotropic traps
We discuss the dissipative dynamics of vortex arrays in trapped
Bose-condensed gases and analyze the lifetime of the vortices as a function of
trap anisotropy and the temperature. In particular, we distinguish the two
regimes of the dissipative dynamics, depending on the relative strength of the
mutual friction between the vortices and the thermal component, and the
friction of the thermal particles on the trap anisotropy. We study the effects
of heating of the thermal cloud by the escaping vortices on the dynamics of the
system.Comment: RevTeX, 8 pages, 3 eps figure
Phase diagram of turbulence in superfluid 3He-B
In superfluid 3He-B mutual-friction damping of vortex-line motion decreases
roughly exponentially with temperature. We record as a function of temperature
and pressure the transition from regular vortex motion at high temperatures to
turbulence at low temperatures. The measurements are performed with
non-invasive NMR techniques, by injecting vortex loops into a long column in
vortex-free rotation. The results display the phase diagram of turbulence at
high flow velocities where the transition from regular to turbulent dynamics is
velocity independent. At the three measured pressures 10.2, 29.0, and 34 bar,
the transition is centered at 0.52--0.59Tc and has a narrow width of 0.06Tc
while at zero pressure turbulence is not observed above 0.45Tc.Comment: To be published in J. Low Temp. Phys. (QFS2004 proceedings
Superfluid Spin-down, with Random Unpinning of the Vortices
The so-called ``creeping'' motion of the pinned vortices in a rotating
superfluid involves ``random unpinning'' and ``vortex motion'' as two
physically separate processes. We argue that such a creeping motion of the
vortices need not be (biased) in the direction of an existing radial Magnus
force, nor should a constant microscopic radial velocity be assigned to the
vortex motion, in contradiction with the basic assumptions of the ``vortex
creep'' model. We point out internal inconsistencies in the predictions of this
model which arise due to this unjustified foundation that ignores the role of
the actual torque on the superfluid. The proper spin-down rate of a pinned
superfluid is then calculated and turns out to be much less than that suggested
in the vortex creep model, hence being of even less observational significance
for its possible application in explaining the post-glitch relaxations of the
radio pulsars.Comment: To be published in J. Low Temp. Phys., Vol. 139, May 2005 [Eqs 11,
15-17 here, have been revised and, may be substituted for the corresponding
ones in that paper
Periodic Vortex Structures in Superfluid 3He-A
We discuss the general properties of periodic vortex arrangements in rotating
superfluids. The different possible structures are classified according to the
symmetry space-groups and the circulation number. We calculate numerically
several types of vortex structures in superfluid 3He-A. The calculations are
done in the Ginzburg-Landau region, but the method is applicable at all
temperatures. A phase diagram of vortices is constructed in the plane formed by
the magnetic field and the rotation velocity. The characteristics of the six
equilibrium vortex solutions are discussed. One of these, the locked vortex 3,
has not been considered in the literature before. The vortex sheet forms the
equilibrium state of rotating 3He-A at rotation velocities exceeding 2.6 rad/s.
The results are in qualitative agreement with experiments.Comment: 13 pages, 7 figures,
http://boojum.hut.fi/research/theory/diagram.htm
Experiments on the twisted vortex state in superfluid 3He-B
We have performed measurements and numerical simulations on a bundle of
vortex lines which is expanding along a rotating column of initially
vortex-free 3He-B. Expanding vortices form a propagating front: Within the
front the superfluid is involved in rotation and behind the front the twisted
vortex state forms, which eventually relaxes to the equilibrium vortex state.
We have measured the magnitude of the twist and its relaxation rate as function
of temperature above 0.3Tc. We also demonstrate that the integrity of the
propagating vortex front results from axial superfluid flow, induced by the
twist.Comment: prepared for proceedings of the QFS2007 symposium in Kaza
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