Quantum crystallization of ${}^4$He is a first-order phase transition from a superfluid liquid and can proceed extremely quickly at very low temperatures. The entropy difference between the two quantum phases, the quantum crystal and superfluid liquid, is small and atoms are carried to the crystal surface via a dissipationless superflow. A limiting process of the transition near absolute zero temperature is quasi-particle scattering off the crystal surface, which is less frequent at lower temperatures. It is known that astonishing interfacial phenomena, such as crystallization wave propagations and total reflection of ultrasound, occur on ${}^4$He crystal surfaces as a result of the rapid crystallization. The rapid crystallization allows the fundamental physics of crystal shape and growth to be examined in a measurable time scale in laboratories, which otherwise cannot be observed in classical crystals. This Colloquium describes far from equilibrium phenomena of significantly deformed ${}^4$He quantum crystals when they were subjected to original driving forces, which are small and usually believed to be irrelevant for ordinary classical crystals. Using driving forces such as gravity, superflow, wettability, acoustic waves, container oscillations, and frictional forces, ${}^4$He crystals were placed under highly non-equilibrium conditions, showing various kinds of extraordinary crystallization and relaxation processes in a superfluid liquid. Rapid crystal shape deformations sometimes influence the surrounding superfluid field in return, resulting in instabilities of the flat crystal surface. Direct visualizations by a high-speed video camera were made, providing an unambiguous observation of the dynamics far from equilibrium of ${}^4$He quantum crystals at very low temperatures.

中文翻译：

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讨论会：超流体中4He的量子结晶远离平衡

的量子结晶 ${}^4$他是超流体液体的一阶相变，可以在非常低的温度下快速进行。量子晶体和超流体液体这两个量子相之间的熵差很小，原子通过无耗散的超流被带到晶体表面。接近绝对零温度的转变的限制过程是准粒子从晶体表面散射，这在较低温度下不那么频繁。众所周知，令人惊讶的界面现象，例如结晶波传播和超声波的全反射，会在${}^4$由于快速结晶，他的晶体表面。快速结晶允许在实验室中的可测量时间范围内检查晶体形状和生长的基本物理原理，否则无法在经典晶体中观察到。这次座谈会描述的远非均衡现象${}^4$当量子晶体受到原始驱动力时，他将其量子化，该驱动力很小，通常被认为与普通的经典晶体无关。利用重力，超流，可湿性，声波，容器振动和摩擦力等驱动力，${}^4$他的晶体放置在高度非平衡的条件下，显示出在超流体液体中各种异常的结晶和弛豫过程。快速的晶体形状变形有时会影响周围的超流场，从而导致平坦晶体表面的不稳定性。通过高速摄像机进行直接可视化，可以清晰地观察到远未达到平衡的动力学。${}^4$他在非常低的温度下量子晶体。