Evidence for magnetic crystallization waves at the surface of $^3$He crystal

TL;DR

This paper presents preliminary experimental evidence for magnetic crystallization waves at the surface of solid $^3$He crystals at ultralow temperatures, supporting theoretical predictions of spin supercurrents in such phenomena.

Contribution

It provides the first experimental support for the existence of magnetic crystallization waves and associated spin supercurrents on the surface of $^3$He crystals.

Findings

Support for the existence of spin supercurrents in melting/freezing waves.

Observation of phenomena below the antiferromagnetic transition temperature.

Evidence of unique inertial properties of the wave involving spin currents.

Abstract

Ultralow temperature crystals of the helium isotopes $^3$He and $^4$He are intriguing quantum systems. Deciphering the complex features of these unusual materials has been made possible in large part by Alexander Andreev's groundbreaking research. In 1978, Andreev and Alexander Parshin predicted the existence of melting/freezing waves at the surface of a solid $^4$He crystal, which was subsequently promptly detected. Successively, for the fermionic $^3$He superfluid/solid interface, even more intricate crystallization waves were anticipated, although they have not been observed experimentally so far. In this work, we provide preliminary results on $^3$He crystals at the temperature $T = 0.41$\;mK, supporting the existence of spin supercurrents in the melting/freezing waves on the crystal surface below the antiferromagnetic ordering temperature $T_N= 0.93$\;mK, as predicted by Andreev. The spin currents that accompany such a melting-freezing wave make it a unique object, in which the inertial mass is distinctly different from the gravitational mass.