Superfluid-like TO Responses in Rotating Solid Helium

TL;DR

This paper investigates the rotational responses of solid helium using a two-frequency torsional oscillator, revealing superfluid-like irrotational behavior that challenges elastic models and supports the supersolid hypothesis.

Contribution

It provides new experimental evidence of superfluid-like responses in solid helium, clarifying previous conflicting results and questioning elastic explanations.

Findings

Most previous rotation experiment results were not reproduced.

Discovered superfluid-like irrotational response in solid helium.

Results cannot be explained by elastic models.

Abstract

The irrotational nature of superfluid helium was discovered through its decoupling from the container under rotation. Similarly, the resonant period drop of a torsional oscillator (TO) containing solid helium was first interpreted as the decoupling of solid from the TO and appearance of supersolid. However, the resonant period can be changed by mechanisms other than supersolid, such as the elastic stiffening of solid helium that is widely accepted as the reason for the TO response. To demonstrate the irrotational nature more directly, the previous experiments superimposed the dc rotation onto the TO and revealed strong suppression on the TO response without affecting the shear modulus. This result is inconsistent with the simple temperature-dependent elasticity model and supports the supersolid scenario. Here, we re-examine the rotational effect on solid helium with a two-frequency rigid TO to clarify the conflicting observations. Surprisingly, most of the result of previous rotation experiments were not reproduced. Instead, we found a very interesting superfluid-like irrotational response that cannot be explained by elastic models.