158 research outputs found
Kelvin-Helmholtz instability of AB interface in superfluid 3He
The Kelvin-Helmholtz instability is well-known in classical hydrodynamics,
where it explains the sudden emergence of interfacial surface waves as a
function of the velocity of flow parallel to the interface. It can be carried
over to the inviscid two-fluid dynamics of superfluids, to study different
types of interfaces and phase boundaries in quantum fluids. We report
measurements on the stability of the phase boundary separating the two bulk
phases of superfluid 3He in rotating flow, while the boundary is localized with
the gradient of the magnetic field to a position perpendicular to the rotation
axis. The results demonstrate that the classic stability condition, when
modified for the superfluid environment, is obeyed down to 0.4 Tc, if a large
fraction of the magnetic polarization of the B-phase is attributed to a
parabolic reduction of the interfacial surface tension with increasing magnetic
field.Comment: 14 pages, 14 figure
Transitions in vortex skyrmion structures in superfluid He-A driven by an analogue of the zero-charge effect
In quantum electrodynamics, the zero-charge effect originates from the
logarithmic dependence of the coupling constant in the action of the
electromagnetic field on the ratio of the ultraviolet and infrared energy
cutoffs. An analogue of this effect in Weyl superfluid He-A is the
logarithmic divergence of the bending energy of the orbital anisotropy axis at
low temperatures, where temperature plays the role of the infrared cutoff and
the vector of the orbital anisotropy plays the role of the vector potential of
the synthetic electromagnetic field for Weyl fermions. We calculate numerically
the spatial distribution of the order parameter in rotating He-A as a
function of temperature. At temperatures close to the superfluid transition, we
observe formation of vortex skyrmions known as the double-quantum vortex and
the vortex sheet. These structures include alternating circular and hyperbolic
merons as a bound pair or a chain, respectively. As temperature lowers towards
absolute zero, we find a continuous transition in the vortex structures towards
a state where the vorticity is distributed in thin tubes around the circular
merons. For the vortex sheet, we present a phase diagram of the transition in
the temperature - angular velocity plane and calculations of the nuclear
magnetic resonance response.Comment: 14 pages, 10 figure
Measurement of Turbulence in Superfluid 3He-B
The experimental investigation of superfluid turbulence in 3He-B is generally
not possible with the techniques which have been developed for 4He-II. We
describe a new method by which a transient burst of turbulent vortex expansion
can be generated in 3He-B. It is based on the injection of a few vortex loops
into rotating vortex-free flow. The time-dependent evolution of the quantized
vorticity is then monitored with NMR spectroscopy. Using these techniques the
transition between regular (i.e. vortex number conserving) and turbulent vortex
dynamics can be recorded at T ~ 0.6 Tc and a number of other characteristics of
turbulence can be followed down to a temperature of T ~ 0.4 Tc.Comment: 31 pages, 10 figure
Microkelvin thermometry with Bose-Einstein condensates of magnons and applications to studies of the AB interface in superfluid He
Coherent precession of trapped Bose-Einstein condensates of magnons is a
sensitive probe for magnetic relaxation processes in superfluid 3He-B down to
the lowest achievable temperatures. We use the dependence of the relaxation
rate on the density of thermal quasiparticles to implement thermometry in 3He-B
at temperatures below 300 K. Unlike popular vibrating wire or quartz
tuning fork based thermometers, magnon condensates allow for contactless
temperature measurement and make possible an independent in situ determination
of the residual zero-temperature relaxation provided by the radiation damping.
We use this magnon-condensate-based thermometry to study the thermal impedance
of the interface between A and B phases of superfluid 3He. The magnon
condensate is also a sensitive probe of the orbital order-parameter texture.
This has allowed us to observe for the first time the non-thermal signature of
the annihilation of two AB interfaces.Comment: 26 pages, 7 figures, manuscript prepared for EU Microkelvin
Collaboration Workshop 2013. Accepted for publication in Journal of Low
Temperature Physic
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