On The Mobile Behavior of Solid $^4$He at High Temperatures

TL;DR

This study investigates the behavior of solid helium inside a torsional oscillator at temperatures between 1.07K and 1.87K, revealing temperature and velocity-dependent decoupling phenomena related to crystal growth conditions.

Contribution

It provides new insights into the mobile behavior of solid helium at high temperatures and how growth conditions affect decoupling in torsional oscillator experiments.

Findings

Decoupled mass fraction reaches ~35% in mixtures at ~1K.

Pure helium crystals show smaller decoupling below 1.3K.

Decoupling depends on temperature, velocity, and growth method.

Abstract

We report studies of solid helium contained inside a torsional oscillator, at temperatures between 1.07K and 1.87K. We grew single crystals inside the oscillator using commercially pure $^4$He and $^3$He-$^4$He mixtures containing 100 ppm $^3$He. Crystals were grown at constant temperature and pressure on the melting curve. At the end of the growth, the crystals were disordered, following which they partially decoupled from the oscillator. The fraction of the decoupled He mass was temperature and velocity dependent. Around 1K, the decoupled mass fraction for crystals grown from the mixture reached a limiting value of around 35%. In the case of crystals grown using commercially pure $^4$He at temperatures below 1.3K, this fraction was much smaller. This difference could possibly be associated with the roughening transition at the solid-liquid interface.