Dynamics of a $$^4$$ 4 He Quantum Crystal in the Superfluid Liquid
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Dynamics of a 4 He Quantum Crystal in the Superfluid Liquid V. L. Tsymbalenko1,2 Received: 18 April 2020 / Accepted: 3 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The motion of helium crystals has been experimentally studied when the crystals fall in the superfluid liquid owing to gravity at temperatures above the roughening transitions where the whole crystal surface is in the atomically rough state. The rate of crystal fall at T = 1.25 K is higher than at T = 1.54 K. This is proof of the essential role of the normal component of superfluid helium in the deceleration of crystal motion. The pressure measurements in the container have shown the effect of surface kinetics on the motions of the crystal and its size. The fall of crystals with the low surface mobility at T = 1.54 K does not change the pressure significantly. The high surface mobility at T = 1.25 K results in decreasing the pressure in the container in the course of the fall of a crystal. The pressure drop exceeds the difference in the hydrostatic pressure between the initial and final positions of the crystal. After the stop, the pressure in the container relaxes to the difference mentioned above. This fact demonstrates an additional growth of the crystal in the flow of a superfluid liquid. Keywords Quantum crystals · Helium · Growth kinetics · Hydrodynamics
1 Introduction The fast kinetics of the atomically rough surfaces of 4 He crystals [1] displays a remarkable interplay between the fluid flow and the superfluid–solid interface. This fact is mentioned by Nozieres and Uwaha [2], and Kagan [3], who theoretically studied the tangential instability of a flat liquid–solid interface. It is found that the instability of the cylindrical crystal shape is associated with the fast interface kinetics. The fluid flow in the direction of the cylindrical axis of a 4 He crystal leads * V. L. Tsymbalenko [email protected] 1
National Research Center “Kurchatov Institute”, Kurchatov Sq. 1, Moscow, Russia 123182
2
Kapitza Institute for Physical Problem RAS, Moscow, Russia 119334
13
Vol.:(0123456789)
Journal of Low Temperature Physics
to developing the instability on the smaller scales [4]. As it concerns the faceted interfacial segments with low mobility, the fluid flow has no observable effect. However, there exist conditions when the crystal facets acquire high mobility comparable with that of the atomically rough surface. Provided that a large overpressure is applied to the crystalline facet, the growth rate of the facet increases drastically by 2–3 orders of magnitude in jump-like manner [5]. At the initial stage the 4 He crystal grows at high growth rates and giant accelerations of the interface. This situation is theoretically analyzed within the framework of the Rayleigh–Taylor and Richtmyer–Meshkov instabilities [6]. The experimental test of theoretical conclusions is complicated by the requirement to prepare the fluid flow with controlled parameters while the 4 He crystal is in the containe
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