K. Izumina

Orientation effect on superfluid 3He in anisotropic aerogel

The orientation of the order parameter in the A-like and B-like phases of superfluid 3He immersed in uniaxially compressed aerogel is reported. With the use of NMR methods, it is found that the orbital momentum of the A-and B-like phases is oriented along the deformation. In the A-like phase, a relatively narrow NMR line with an anomalously large negative frequency shift is observed. The Leggett frequency in the A-like phase, which shows the same energy gap suppression as in the B-like phase, is measured.

Coherent precession of magnetization in the superfluid 3He A-phase.

We report the first observation of coherent precession of magnetization in superfluid 3He A-like phase (CP-A) in aerogel. The coherent precession in bulk 3He A-phase is unstable due to the positive feedback of spin supercurrent to the gradient of phase of precession. It was predicted that the homogeneous precession will be stable if the orbital momentum of the 3He A-phase can be oriented along the magnetic field. We have succeeded to prepare this configuration by emerging 3He in uniaxially deformed anisotropic aerogel. The dissipation rate of coherent precession states in aerogel is much larger than that in bulk 3He B-phase. We propose a mechanism of this dissipation.

Growth of a single vortex line of 3He-A in a narrow cylinder under rotation

We have studied a single vortex in superfluid 3He-A in a single narrow cylinder under rotation. The diameter of the cylinder is 230 μm. We observed the growth of a single vortex line in the cylinder by rotation. The vortex line grows along the cylinder when the rotation speeds are linearly accelerated above a critical velocity, which are about 4 (rad/sec).

Rotating Superfluid 3He‐A in Parallel‐Plate Geometry

We have measured NMR spectra of the 3He‐A phase restricted between parallel plates under rotation at a speed of Ω < 6.28 rad/s, using a rotating cryostat at ISSP. The sample volume was divided by the plates into 110 disk‐shaped spaces, each with a thickness of 12.5 μm and a radius of 1.5 mm. They were connected to a bulk superfluid through 0.3 mm‐wide channels. Measurements were done by continuous wave (cw) NMR at 869 kHz. The axes of both H and Ω were perpendicular to the parallel plates. We observed a very narrow spectrum with a negative frequency shift, an indication that the gaps and the superfluid texture were well designed.

Effect of the cooling speed through Tc on the formation of textures in superfluid 3He-A

The cw-NMR measurements have been performed for superfluid 3He A-phase in a single cylinder with 115 μm inner radius. We observed two peaks in NMR spectra, the main peak and the satellite peak. The satellite peak is attributed to textures which are induced by the flow due to temperature gradient by controlling the cooling speed of samples from normal fluid state to superfluid A-phase. We have observed that the satellite peak height of NMR spectrum increases continuously as the cooling speed increases. The number of possible texture types is restricted for our cylindrical cell, since the radius of the cell is about ten times larger than the dipole coherence length ξd ~ 10 μm. Therefore, it is unlikely that the continuous change of NMR spectrum is attributed to the different kinds of textures. We discuss that these results are due to textural domain structure along cylindrical axis.

Coherent precession of magnetization in superfluid 3He A-phase in aerogel

The coherent precession in bulk 3He A-phase is unstable due to the positive feedback of spin supercurrent to the gradient of phase of precession. It was predicted that the homogeneous precession will be stable if the orbital momentum could be oriented along the magnetic field. [7] We have found that the orbital part of order parameter in 3He A-phase immersed in aerogel orients along the direction of aerogel axial squeezing. By this method we have oriented the orbital momentum of 3He A-phase along the magnetic field and studied non-linear NMR properties. By cw-NMR we have succeeded to form the state with Coherent Precession in 3He A-phase (CP-A), which is analog of Homogeneous Precession Domain (HPD) in 3He B-phase. We have found that the dissipation of CP-A and HPD in aerogel is much larger than in bulk superfluid 3He and depends from sample to sample. We propose a model to explain enhancement of the dissipation in CP-A, which takes into account the spin diffusion of inhomogeneous magnetization created by fluctuations of the condensation energy of Cooper pair in aerogel.

Vortex State of 3He‐A Studied by NMR Linewidth

The vortex state of superfluid 3He‐A has been studied under rotation by measuring the change of the width of the main NMR line at rotation speeds up to twice as fast as previously reported. We identify three temperature ranges according to the temperature dependence of the linewidth. These temperature ranges have been predicted by Fomin and Kamenskii. We also report the results of our preliminary NMR linewidth measurements for different rotational speed Ω’s. These are consistent with previously reported results, where they overlap, and reveal a different Ω dependence for each temperature range.