Quantum crystal oscillations in a superfluid liquid

TL;DR

This paper investigates the hydrodynamics of quantum helium crystal oscillations in superfluid helium, revealing a temperature-dependent transition in the reaction force and identifying a new hydrodynamic instability at high oscillation velocities.

Contribution

The study introduces a model describing quantum helium crystal oscillations in superfluid helium, validated by experiments, and uncovers a novel hydrodynamic instability at certain velocities.

Findings

Reaction force shifts from inertial to viscous as temperature decreases.

Experimental validation of the model within 0.54-1.43 K.

Discovery of a new hydrodynamic instability at velocities above ~3 cm/s.

Abstract

We study the hydrodynamics of quantum 4He crystal oscillations in a superfluid liquid with involving the dynamics of atomically rough surfaces. It is shown that, due to enhancement of the kinetic growth coefficient as the temperature lowers, the reaction force of the liquid applied to the 4He crystal changes its character from the inertial to the viscous one vanishing as T->0. The model is confirmed by the experiments on the oscillations of the 4He crystal within the temperature range 0.54 - 1.43 K at frequencies 484 and 211 Hz. New type of a hydrodynamic instability is found. The instability occurs provided that the oscillation amplitude of the velocity becomes higher than ~3 cm/s.