Disorder and the Supersolid State of Solid $^4$He

TL;DR

This study investigates the relationship between disorder and supersolidity in solid $^4$He, showing that highly disordered or glassy samples exhibit large supersolid signals, unlike high-quality crystals.

Contribution

It demonstrates that supersolidity in solid $^4$He is strongly associated with disorder, particularly in rapidly frozen, amorphous samples, contrasting with the absence in well-annealed crystals.

Findings

Large supersolid signals (>20%) in rapidly frozen disordered samples

Supersolid signals diminish with annealing in high-quality crystals

Supersolidity correlates with disorder or glassy state of solid helium

Abstract

We report torsional oscillator supersolid studies of highly disordered samples of solid $^4$He. In an attempt to approach the amorphous or glassy state of the solid, we prepare our samples by rapid freezing from the normal phase of liquid $^4$He. Less than two minutes is required for the entire process of freezing and the subsequent cooling of the sample to below 1 K. The supersolid signals observed for such samples are remarkably large, exceeding 20 % of the entire solid helium moment of inertia. These results, taken with the finding that the magnitude of the small supersolid signals observed in our earlier experiments can be reduced to an unobservable level by annealing, strongly suggest that the supersolid state exists for the disordered or glassy state of helium and is absent in high quality crystals of solid $^4$He.