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Using NMR techniques we monitor the structure and number of vortices in a cylindrical container, rotating at constant angular velocity Ω, before and after the passage of the A-B interface. The initial A phase contains the equilibrium number of vortices. The final B phase is found to have a deficit of vortices which depends nonmonotonically on the measured time t AB of the A→B transition. We argue that a vortex layer is formed in front of the moving A-B interface. The measured vortex deficit can be understood by analyzing the stability of the layer

Insight in the dynamics of quantized vortex lines has been obtained by performing NMR measurements in uniformly rotating superfluid [sup 3]He-[ital B]. Compared to superfluid [sup 4]He, in [sup 3]He-[ital B] the viscosity of the normal component is three orders of magnitude larger and the pinning of vortices is weaker. The collective modes governing the hydrodynamic response of an array of vortex lines are highly overdamped. Two distinct modes are identified: (1) a relatively fast mutual-friction-resisted mode, which controls the redistribution of the vortex density on a time scale of a few seconds, and (2) an exponentially relaxing slow mode with a time constant of a few minutes, which governs asymptotically the approach to equilibrium at nearly constant vortex density. Measurement of the fast motion allows us to extract the dissipative mutual friction. The slow mode is dominated by the elastic tension along the vortex line and by weak pinning at the top and bottom surfaces of the rotating container. With increasing vortex density the surface pinning becomes a collective process, in which coherently moving groups of vortices are pinned in unison. Collective pinning is a result of the shear elasticity related to the crystalline order of the vortex lattice.more » Our measurements on the slow mode indicate that the crystalline correlation extends over many lattice spacings.« less

We have observed spin-mass vortices (SMV) in rotating superfluid $^{3}\mathit{B}$. The SMV is a combined topological object formed of an ordinary vortex with mass current and of a disclination with spin current. A planar defect, so-called \ensuremath{\theta} soliton, is topologically bound to the SMV line. The SMV's were created primarily by cooling the $^{3}\mathrm{He}$ sample through a reversible A\ensuremath{\rightarrow}B transition at a constant rotation velocity, which was smaller than the critical velocity for the nucleation of vortices ${\mathrm{in}}^{3}$He-B. The observation of the SMV's is based on changes in the NMR absorption caused by the attached solitons: The absorption is shifted to higher frequencies in conventional NMR at low rf excitation and large additional absorption is observed in the homogeneously precessing domain (HPD) at high excitation. The presence of SMV's is deduced from the stability and from the rotation-speed dependence of the additional absorption.

In transverse NMR at high rf excitation, it is possible to separate a [sup 3]He-[ital B] sample into two magnetic domains. In one domain the spins are precessing coherently with a large tilting angle in relation to the polarizing magnetic field while in the other they are stationary and oriented parallel to the field. We have studied the two-domain system during vortex-free rotation and found that the boundary region between the precessing and static domains is sensitive to superfluid counterflow, flowing parallel to the boundary. The volume of the precessing domain decreases and the NMR absorption, associated with spin diffusion across the boundary, increases. The shift of the domain boundary is analyzed in terms of the competition between the kinetic energy of counterflow and the gradient in the Zeeman energy. From the shift we obtain the superfluid density anisotropy, induced by the magnetic field. A calculation in the weak-coupling approximation explains only half of the measured ansiotropy at low pressures. At high pressures the discrepancy is smaller.

We have observed spin-mass vortices (SMV) in superfluid $^{3}\mathit{B}$. The SMV is a combined topological object made up of a vortex line with mass current and a disclination line with spin current. It is also a termination line of a planar defect, the so-called \ensuremath{\theta} soliton. The SMVs are bound either as pairs or to the container wall by the soliton. They are nucleated when a rotating $^{3}\mathrm{He}$ sample cools slowly through the A\ensuremath{\rightarrow}B phase transition. The identification of the SMV is based on the NMR signatures of the soliton.

We present experimental proof that in rotating {sup 3}He-{ital B} the vortex-core transition temperature {ital T}{sub {ital V}} separates axisymmetric vortices above {ital T}{sub {ital V}} from vortices with spontaneously broken axial symmetry below {ital T}{sub {ital V}}. The nonaxisymmetry is observed in the presence of coherent spin precession as a new soft Goldstone mode, manifested as oscillations and spiral twisting of the core anisotropy axis. These are driven by the precessing spin via spin-orbit coupling and lead to magnetic relaxation from viscous losses, which depend on vortex pinning.

The order-parameter texture has been studied in rotating {sup 3}He-{ital B} in the vortex-free state with NMR techniques. A sequence of textural phase transitions is observed with increasing rotation speed. It is generated by competing interactions with magnetic field, surfaces, and rotation. Two surface interactions are extracted: the susceptibility anisotropy at the wall and the gyromagnetism due to a magnetic-field-induced surface supercurrent. The results are consistent with an order-parameter structure approaching the planar state with diffuse quasiparticle scattering at the wall.

Experiments with negative ions in rotating superfluid 3He-A show strong retardation and deformation of ion pulses drifting parallel to the angular velocity Ω. This is caused by the interaction between the ions and the l texture in the soft cores of A-phase vortices. The interaction is mediated by the anisotropic ion mobility: v=μ⊥E-Δμ(E·l)l. The (Ω,T) dependence of the retardation is explained by a model that assumes focusing of ions into the vortex cores, along which the mobility μc is lower than that in the bulk liquid, μ⊥. We find μc=μ⊥-0.6Δμ.

First experiments suggesting the presence of singular vortices in rotating /sup 3/He-A are reported. Our studies on the interaction between negative ions and vortex textures verify the existence of the continuous vortices seen earlier by NMR, but evidence for a new vortex state with high ion mobility along the core is also found. The nucleation of the new vortex depends on the external magnetic field and the rotation history of the sample.