Abstract
Quantum crystallization of is a first-order phase transition from a superfluid liquid and can proceed extremely quickly at particularly 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 quasiparticle scattering off the crystal surface, which is less frequent at lower temperatures. It is known that interfacial phenomena, such as crystallization wave propagations and total reflection of ultrasound, occur on 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 timescale in laboratories, which otherwise cannot be observed in classical crystals. This Colloquium describes far from equilibrium phenomena of significantly deformed quantum crystals when they are 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, crystals are placed under highly nonequilibrium 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 are made, providing an unambiguous observation of the dynamics far from equilibrium of quantum crystals at extremely low temperatures.
18 More- Received 9 December 2019
DOI:https://doi.org/10.1103/RevModPhys.92.041003
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