Studies on crystal growth of nuclear-ordered solid ^3He at ultra-low temperature

对超流^3He中的有序核固体^3He在超低温下的晶体生长（和熔化）的研究将探索晶体生长的详细和微观机制，因为有序核固体的凝固潜热变得非常小，并且过剩保证了晶体生长和熔化过程中良好的热量和质量传输，以及已经深入研究的^4He情况。^3He情况的独特之处在于自旋超电流对晶体生长的主要贡献，因为固体和液体之间存在着很大的磁化差。(1)We在1 mm phi圆柱形样品池中研究了核有序^3He的晶体生长和熔化，发现生长速率和熔化速率有很大差异。超流B相的生长机制为螺位错辅助生长机制，台阶速度受超流B相的破偶速度限制。另一方面，融化的速度非常快，我们还不能测量任何定量数据， 关于我们 熔化过程中的固体表面似乎是一个粗糙的表面。进一步的研究是通过使用下文所述的核磁共振成像技术（MRI）的进展。（2）研究了固体在过冷液态^4He中的形核问题。as a function函数of temperature温度.我们发现成核速率变得与温度无关，并得出成核是通过量子隧穿机制发生的结论。我们将把这项研究扩展到超低温下^3He的情况。(3)We研究了多孔介质中^4He在超流状态下的冻胀问题。提出了霜层生长的耗散机制，并与已有的实验结果进行了比较。(4)We开发了适用于超低温的MRI技术。我们应用MRI显示^3He-^4He相分离边界。我们通过这种技术实现了约10妈妈的2维空间分辨率。（5）结合上述核磁共振谱，研究了核有序固体^3 He的自旋动力学，观察到了一定条件下核磁共振均匀模式的苏尔不稳定性。少

Studies of crystal growth (and melt) of nuclear-ordered solid ^3He in superfluid ^3He at ultra-low temperatures will explore detailed and microscopic mechanisms of crystal growth since latent heat of solidification of nuclear-ordered solid becomes very small and superfluity guarantee good heat and mass transport during crystal growth and melt as well as the ^4He case which has been studied thoroughly. Unique feature of the ^3He case is the dominant contribution of spin supercurrent to the crystal growth since there exists a large magntization difference between solid and liquid.(1)We studied crystal growth and melt of nuclear-ordered ^3He in 1 mmphi cylindrical sample cell and found a large difference of the rates of growth and melt. The growth mechanism should be the screw-dislocation assisted one and the step velocity is limited by the pair-breaking velocity of superfluid B phase. On the other hand, the melt is rather very fast and we could not measure any quantitative data yet but t … More he surface of the solid on the melting process seems to be a rough surface. Further research is on progress by using the NMR-imaging technique (MRI) described below.(2)The nucleation problem of solid in a supercooled liquid ^4He has been investigated. as a function of temperature. We found that the nucleation rate becomes temperature-independent and concluded that nucleation occured by quantum tunneling mechanism. We will extend this studies to the ^3He case at ultra-low temperatures.(3)We studied frost heave of ^4He from porous media when ^4He is in the superfuild state. We proposed the dissipation mechanism of the growth of frost and compared it with our data.(4)We developed the MRI technique applicable at ultra-low temperatures. We applied the MRI to visualize ^3He-^4He phase separation boundary. We achieved 2-dimensional space resolution of about 10 mum by this technique.(5)With connection of the above MRI,spin dynamics of nuclear-ordered solid ^3He has been stueied and the Suhl instability of the uniform mode of NMR was observed under certain conditions. Less