On the origin of the decrease in the torsional oscillator period of solid He4

TL;DR

This paper suggests that the observed decrease in torsional oscillator period of solid He4 may be due to glass formation from liquid-like components, offering an alternative to the supersolid explanation.

Contribution

It proposes that low-temperature glass formation from liquid-like components explains the period decrease, challenging the supersolid interpretation.

Findings

The period decrease is consistent with solidification into a low-temperature glass.

The glass formation explains the dissipation peak near the transition.

External parameter dependence supports the glass hypothesis.

Abstract

A decrease in the rotational period observed in torsional oscillator measurements was recently taken as a possible indication of a supersolid state of helium. We reexamine this interpretation and note that the decrease in the rotation period is also consistent with a solidification of a small liquid-like component into a low-temperature glass. Such a solidification may occur by a low-temperature quench of topological defects (e.g., grain boundaries or dislocations) which we examined in an earlier work. The low-temperature glass can account for not only a monotonic decrease in the rotation period as the temperature is lowered but also explains the peak in the dissipation occurring near the transition point. Unlike the non-classical rotational inertia scenario, which depends on the supersolid fraction, the dependence of the rotational period on external parameters, e.g., the oscillator velocity, provides an alternate interpretation of the oscillator experiments. Future experiments might explore this effect.