204 research outputs found
Comment on 'Nucleation of 3He-B from the A Phase: A Cosmic-Ray Effect?'
A comment to the article by Leggett, A. J.Peer reviewe
Quasiparticle scattering measurements of laminar and turbulent vortex flow in the spin-down of superfluid 3He-B
The dynamics of quantized vortices is studied in superfluid 3He-B after a
rapid stop of rotation. We use Andreev reflection of thermal excitations to
monitor vortex motion with quartz tuning fork oscillators in two different
experimental setups at temperatures below 0.2Tc. Deviations from ideal
cylindrical symmetry in the flow environment cause the early decay to become
turbulent. This is identified from a rapid initial overshoot in the vortex
density above the value before the spin-down and its subsequent decay with a
t^(-3/2) time dependence. The high polarization of the vortices along the
rotation axis significantly suppresses the effective turbulent kinematic
viscosity below the values reported for more homogeneous turbulence and leads
to a laminar late-time response. The vortex dissipation down to T < 0.15Tc is
determined from the precession frequency of the polarized vortex configuration.
In the limit of vanishing normal component density, the laminar dissipation is
found to approach a temperature-independent value, whose origin is currently
under discussion.Comment: 8 pages, 5 figure
Continuous Vortices with Broken Symmetry in Rotating Superfluid 3He-A
New NMR measurements are reported on continuous 3He-A vortices in tilted magnetic fields. We introduce a symmetry classification of the continuous vortices with broken axial symmetry. It is found that the discrete internal symmetry may in addition be broken in two inequivalent ways, producing two different continuous vortices. Although NMR may not distinguish between these two vortices, the observed vortex satellite peak is well accounted for by spin waves localized in the soft core of such vortices.Peer reviewe
Vortex core transitions in superfluid 3He in globally anisotropic aerogels
Core structures of a single vortex in A-like and B-like phases of superfluid
3He in uniaxially compressed and stretched aerogels are studied by numerically
solving Ginzburg-Landau equations derived microscopically. It is found that,
although any uniaxial deformation leads to a wider A-like phase with the axial
pairing in the pressure-temperature phase diagram, the vortex core states in
the two phases in aerogel depend highly on the type of deformation. In a
compressed aerogel, the first-order vortex core transition (VCT) previously
seen in the bulk B phase appears at any pressure in the B-like phase while no
strange vortex core is expected in the corresponding A-like phase. By contrast,
in a stretched aerogel, the VCT in the B-like phase is lost while another VCT
is expected to occur between a nonunitary core and a polar one in the A-like
phase. Experimental search for these results is hoped to understand correlation
between superfluid 3He and aerogel structure.Comment: 7 pages, 6 figures Text was changed. Resubmitted versio
Structure of surface vortex sheet between two rotating 3He superfluids
We study a two-phase sample of superfluid 3He where vorticity exists in one
phase (3He-A) but cannot penetrate across the interfacial boundary to a second
coherent phase (3He-B). We calculate the bending of the vorticity into a
surface vortex sheet on the interface and solve the internal structure of this
new type of vortex sheet. The compression of the vorticity from three to two
dimensions enforces a structure which is made up of half-quantum units,
independently of the structure of the source vorticity in the bulk. These
results are consistent with our NMR measurements.Comment: 4 pages, 4 figure
Defect Formation in Quench-Cooled Superfluid Phase Transition
We use neutron absorption in rotating 3He-B to heat locally a 10
micrometer-size volume into normal phase. When the heated region cools back in
microseconds, vortex lines are formed. We record with NMR the number of lines
as a function of superflow velocity and compare to the Kibble-Zurek theory of
vortex-loop freeze-out from a random network of defects. The measurements
confirm the calculated loop-size distribution and show that also the superfluid
state itself forms as a patchwork of competing A and B phase blobs. This
explains the A to B transition in supercooled neutron-irradiated 3He-A.Comment: RevTex file, 4 pages, 3 figures, resubmitted to Phys. Rev. Let
Human recombinant interleukin-1 regulates cellular mRNA levels of dermatan sulphate proteoglycan core protein
Unconventional Vortices and Phase Transitions in Rapidly Rotating Superfluid ^{3}He
This paper studies vortex-lattice phases of rapidly rotating superfluid ^3He
based on the Ginzburg-Landau free-energy functional. To identify stable phases
in the p-Omega plane (p: pressure; Omega: angular velocity), the functional is
minimized with the Landau-level expansion method using up to 3000 Landau
levels. This system can sustain various exotic vortices by either (i) shifting
vortex cores among different components or (ii) filling in cores with
components not used in the bulk. In addition, the phase near the upper critical
angular velocity Omega_{c2} is neither the A nor B phases, but the polar state
with the smallest superfluid density as already shown by Schopohl. Thus,
multiple phases are anticipated to exist in the p-Omega plane. Six different
phases are found in the present calculation performed over 0.0001 Omega_{c2} <=
Omega <= Omega_{c2}, where Omega_{c2} is of order (1- T/T_c) times 10^{7}
rad/s. It is shown that the double-core vortex experimentally found in the B
phase originates from the conventional hexagonal lattice of the polar state
near Omega_{c2} via (i) a phase composed of interpenetrating polar and
Scharnberg-Klemm sublattices; (ii) the A-phase mixed-twist lattice with polar
cores; (iii) the normal-core lattice found in the isolated-vortex calculation
by Ohmi, Tsuneto, and Fujita; and (iv) the A-phase-core vortex discovered in
another isolated-vortex calculation by Salomaa and Volovik. It is predicted
that the double-core vortex will disappear completely in the experimental p-T
phase diagram to be replaced by the A-phase-core vortex for Omega >~ 10^{3} ~
10^{4} rad/s. C programs to minimize a single-component Ginzburg-Landau
functional are available at {http://phys.sci.hokudai.ac.jp/~kita/index-e.html}.Comment: 13 pages, 9 figure
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