Studies of Nuclear-Ordered Solid ^3He by using Ultrasonic Sound

由于导致固体^3He中核有序的主要相互作用是^3He原子之间的直接交换过程，所以核自旋系统与晶格强耦合。因此，同时用核磁共振和超声方法研究核有序固体~3He是非常有意义的。预计在核有序温度下声速将发生变化，声速对磁各向异性轴的各向异性，以及由于磁声和光模的共振吸收以及多次磁振子散射引起的声衰减。我们成功地制备了具有单一磁畴的大尺寸固体^3He单晶，并将其冷却到100muK温度范围。我们获得了以下结果：(1)核磁共振测量：我们在核有序的~3He的低场相进行了脉冲核磁共振，并研究了其非线性自旋动力学。我们发现原子核…的匀速运动更多的r自旋在低温、低外加磁场下变得不稳定，并且自旋从平衡构型向大倾角倾斜。我们在自旋运动稳定的区域观察到了多个自旋回波，并可以研究相干偶极矩的详细形式。通过磁子热涨落的重整化，成功地解释了共振频率的微小负移。(2)晶体生长：为了生长高质量的~3He单晶，我们研究了超流~3He中核有序固体~(3)He的晶体生长和熔化。我们发现晶体生长和熔化的速度有很大的不同。生长可能受到与螺位错有关的生长机制的控制，而熔体在粗糙表面上的生长机制类似于^4He。(3)声学实验：搭建了声速和衰减测量系统。我们对声速变化的分辨率是一次测量的几个10ppm。我们完成了一个Sound小室，研究了单结晶体和单结晶体上的核磁共振-声音同时测量。较少

Since the main interaction to cause the nuclear-ordering in solid ^3He is a direct exchange processes between ^3He atoms, the nuclear spin system is strongly coupled with a lattice. Therefore, it is very interesting to study nuclear-ordered solid ^3He by using both nuclear magnetic resonance and ultrasonic methods simultaneously. It is expected that there will be a change of the sound velocity at the nuclear-ordering temperature, anisotropy of the sound velocity against the magnetic anisotropy axis, and sound attenuation due to resonant absorption of the magnetic acoustic and optical modes and due to multiple magnon scattering.We succeeded in making a large single crystal of solid ^3He with a single magnetic domain and in cooling it to 100muK temperature range. We obtained the following results for this project :(1) NMR measurement ; We took pulsed NMR in the low field phase of the nuclear-ordered ^3He and studied the non-linear spin dynamics. We found that the uniform motion of nuclea … More r spin became unstable in low temperatutes, low applied fields and for a large tipping of spins from an equilibrium configuration. We observed multiple spin echoes in the regions where spin motion was stable and could study the detailed form of the coherent dipole torque. We succeeded in explaing the small negative shift of resonant frequency by renormalizing the thermal fluctuation of magnons.(2) Crystal growth ; In order to grow a single crystal of ^3He of good quality, we studied crystal growth and melt of nuclear-ordered solid ^3He from superfluid ^3He. We found that the rates of crystal growth and melt were quite different. The growth may be controlled by growth mechanisms related to the screw dislocation and the melt by mechanisms similar to ^4He on rough surfaces.(3) Sound experiment ; We constructed the sound velocity and attenuation measuring system. Our resolution of the change in sound velocity was several 10 ppm by one shot of measurement. We completed a sound cell to investigate the NMR-sound simultaneous measurement on a single and mono-domain crystal. Less