Observation of half-quantum defects in superfluid 3He-B

In the course of high-precision measurements of the relation between the superflow current J through a weak link in 3He-B and the difference in order parameter phase between each side of the link phi in a flexible wall Helmholtz resonator equipped with a rotation pickup loop, we have observed the signature of a stable textural defect that sustains a change of the phase by pi across it. "Cosmiclike" solitons, proposed by Salomaa and Volovik and hitherto thought unstable, can constitute such a defect.     

Magnetoacoustic spectroscopy in superfluid 3He-B

We have used the acoustic Faraday effect in superfluid 3He to perform high resolution spectroscopy of an excited state of the superfluid condensate, called the imaginary squashing mode. With acoustic cavity interferometry we measure the rotation of the plane of polarization of a transverse sound wave propagating in the direction of the magnetic field from which we determine the Zeeman energy of the mode. We interpret the Landé g factor, combined with the zero-field energies of this excited state, using the theory of Sauls and Serene, to calculate the strength of f-wave interactions in 3He.     

Spinning particle-like solitons in superfluid3He-B

Particle-like topological solitons in superfluid³He-B are studied. The existing treatment of such objects indicates that static solitons have a free energy proportional to their size. They are thus unstable and will shrink to zero size. In the present work we consider spinning solitons whose size originates from an angular momentum barrier. In order for the solitons to be meaningfully described by theB phase their free energy must be small compared with their condensation energy. This requires that the angular momentum be large and effectively they are in the classical continuum limit. A detailed consideration of the variational procedure required to determine the soliton profile is presented allowing estimates of their size and energy. Address as from October 1991: Physics Institute, Faculty of Liberal Arts, Shizuoka University, Shizuoka 422, Japan     

Spin precession waves in superfluid 3He-B

Spin precession waves of homogeneously precessing domains (HPD) in superfluid 3He-B have been studied at 11 bars and temperatures down to 0.45T(c). The waves were excited by an alternating longitudinal magnetic field with an axial symmetry, applied as a small perturbation ranging from 1 nT up to a few micro T. When the spin precession wave is excited, two nuclear magnetic resonances simultaneously coexist: first, the high frequency resonance used for excitation of the HPD, and, second, the low-frequency resonance of the HPD wave mode. We report the first experimental evidence of the nonlinear behavior of low-frequency precession spin wave modes of the continuously maintained HPD.     

Decay of pure quantum turbulence in superfluid 3He-B

We describe measurements of the decay of pure superfluid turbulence in superfluid 3He-B, in the low temperature regime where the normal fluid density is negligible. We follow the decay of the turbulence generated by a vibrating grid as detected by vibrating wire resonators. Despite the absence of any classical normal fluid dissipation processes, the decay is consistent with turbulence having the classical Kolmogorov energy spectrum and is remarkably similar to that measured in superfluid 4He at relatively high temperatures. Further, our results strongly suggest that the decay is governed by the superfluid circulation quantum rather than kinematic viscosity.     

Parametric instability in uniform spin precession in superfluid 3He-B

In order to explain the “catastrophic spin relaxation” observed in superfluid ³He-B, the stability of spatially uniform spin precession in this liquid relative to the parametric excitation of spin waves has been analyzed. It is shown that uniform spin precession becomes unstable at low temperatures (Suhl instability). At zero temperature, the growth increments are determined for all spin wave branches. The temperature at which the transition from stable spin precession to instability takes place is estimated.     

Diaphragm-driven flow in rotating superfluid He-B

We present the theory used to analyse experiments at Manchester University in which we observe the normal modes of transverse vibration of a Kapton diaphragm separating two nominally identical disc-shaped regions of superfluid ³He, each of height 100 μm and diameter 40 mm. From the mode frequencies we deduce information on the superfluid density and hence on strong coupling corrections to the energy gap. From the dissipation the first and second viscosities, η and ξ₃, of the fluid can be obtained. Rotation of the experiment about an axis perpendicular to the diaphragm creates a lattice of quantised vortex lines. We show how the mutual friction parameters B and B′ can be determined from the effect of the vortices on the normal modes of the diaphragm.     

Repetitive single vortex-loop creation by a vibrating wire in superfluid 3He-B

Spectacular features are observed on the velocity-force characteristics of a vibrating wire resonator in superfluid 3He-B at ultralow temperatures. Both plateaus and discontinuities are seen in the characteristics. The plateaus seem to have two separate critical velocities where first some "event" occurs, which causes the wire to lose energy and slow down, followed by a second lower critical velocity where the event decouples. It is suggested that these events are due to vortex-loop creation at protuberances on the vibrating wire. This opens up the possibility of controlling the creation of vorticity through specially prepared protuberances.