Studies on Quantum Fluid Dynamics of Rotating Superfluid Helium-3

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By using a rotating ultra-low temperature cryostat constructed at Institute for Solid State Physics, which rotates at the word-highest rotation speed of 1 rotation/sec and cools the ^3He sample down to sub mK temperatures, we studied 1)fluid dynamics of superfluid-A phase in two kinds of cylindrical sample cells with 0.1 mm and 0.2 mm diameters. For the case of 0.1 mm diameter sample cell, we succeeded to control 3 kinds of textures by rotation, cooling conditions, and magnetic fields. One of these textures was found to be the Mermin-Ho textures(M-H). We observed a spin wave signal localized at the soft core of the M-H by NMR and from rotation dependence of the spin wave frequency, we concluded that a macroscopic angular momentum attached to the soft core,. The macroscopic angular momentum may come from the intrinsic angular momentum of Cooper pair in A-phase. For the case of 0.2 diameter sample, we observed two kinds of textures (probably the M-H and Disgyration textures). As increasi … More ng a rotation speed in the M-H, the M-H first flips from n=-1 to n=+1 by introduction of a vortex with n=2 in the cylinder. As further increasing the rotation speed, a vortex with n=2 is introduced to the M-H with n=+1. We discussed the nucleation and annihilation of quantized vortices. We could control the two textures of the M-H and the Disgyration by relative orientation between the rotation and magnetic field when we cooled the sample through the superfluid transition temperature T_c. This is a kind of Einstein-Barnett effectand there is not yet any explanation. 2)quantized vortex in superfluid ^3He in aerogel porous material under rotation. In A-phase, the structure of the vertex can be a singular one with a core size of the coherence length of ξ_0. In B-phase, we observed the quantum vortex introduced to the aerogel but the vortices were strongly pinned by aerogel. The pinning maintained super-current for a long time even after the rotation was stopped. This behavior is resembled to the creep phenomena of quantized flux in very hard type II superconductors. We studied pinning and creation of vortices in aerogel. 3)search for a new vortex in superfluid a-phase in a narrow parallel plate with a spacing smaller than the dipole coherence length of 10 μm. In this sample cell, the l-and d-vector of the order-parameter are perpendicular with each other. This configuration is different from a bulk superfluid. When the rotation speed increased, Freedericksz transition occurred. Further increasing the rotation, then vortex started to go into the sample. From the large value of the critical velocity of nucleation of the vortex, we speculated that the vortex should be the phase vortex with the core size of ξ_0. Less