Falling⁴He crystals in superfluid

Abstract

The crystal shapes of 4 He falling in superfluid were investigated using a high speed video camera. As they fell, the upper surface of the crystal became rough and the lower surface became faceted as a result of being subjected to an upward superflow which induced melting of the upper surface and crystallization of the lower surface. When it landed on the bottom, a pulse-like wave was observed to travel around the surface from the impact point before it transformed itself quickly to adjust to a new boundary condition. The behavior of a crystal when it passed by a small needle during its fall was also observed. The rim of the facet was pulled by the needle and protruded. The origin of this extended deformation is not understood at present, but the superflow around the crystal was possibly the origin of the interaction between the crystal and the needle.S Online supplementary data available from stacks.iop.org/njp/16/113022/ mmedia

Asymmetry in melting and growth relaxation of4He crystals in superfluid after manipulation by acoustic radiation pressure

“…In the metastable superfluid at a few millibar above the melting pressure, an acoustic wave pulse was applied by the upper transducer to initiate nucleation of a hexagonal-closed-packed (hcp) 4 He seed crystal on the transducer surface [13,21,30]. The crystal eventually fell in the superfluid and landed on the bottom.…”

Quantum viscosity and the Reynolds similitude in quantum liquid He-II

“…The accuracy of our theory will be improved through future measurements of the drag force or the effective dynamic viscosity η ′ n on an object with various shapes in a wide range of temperatures. Furthermore, more experimental data under higher pressures is required to facilitate precise extension of the theory to the systems of 4 He crystal [12,[46][47][48][49]. As in the experiments, we can track the detailed motion of falling objects in He-II and extract more useful information regarding the terminal speed and the property of the chaotic motion owing to the turbulent wake of the superfluid component.…”

The Effect of the Interphase Kinetics on the Motion of a Quantum Crystal in Superfluid Liquid

“…The phase kinetics plays a significant role even at the magnitudes of the kinetic growth coefficient K ∼ 0.2s/m. The question whether this model is applicable to the interpretation of the experiments of the Japanese group [6] should be answered negatively. The lower part of the crystal, as is seen in the shooting, has the well-visible facets.…”

“…The direct observation of the crystal shape transformation during the fall of the crystal is made by the Japanese group at 0.3 K using a high-speed camera [6]. The acceleration at which the crystal falls corresponds to the motion of a solid body with the adjoined mass equal to the mass of a half of the liquid displaced by the crystal.…”