Interplay of Rotational, Relaxational, and Shear Dynamics in Solid 4He

TL;DR

This study investigates the microscopic excitations in solid helium-4 using torsional oscillator techniques, revealing that their dynamics are independent of supersolid transition theories and are linked to shear responses.

Contribution

It demonstrates that the excitations responsible for torsional oscillator behavior are generated independently of supersolidity and are related to shear modulus changes, challenging existing supersolid models.

Findings

Relaxation times diverge smoothly without critical points.

TO response and shear modulus share identical temperature-velocity and temperature-strain dependencies.

Microscopic excitations are generated by thermal and mechanical stimuli independently.

Abstract

Using a high-sensitivity torsional oscillator technique, we mapped the rotational and relaxational dynamics of solid helium-4 throughout the parameter range of the proposed supersolidity. We found evidence that the same microscopic excitations controlling the torsional oscillator motions are generated independently by thermal and mechanical stimulation. Moreover, a measure for the relaxation times of these excitations diverges smoothly without any indication for a critical temperature or critical velocity of a supersolid transition. Finally, we demonstrated that the combined temperature-velocity dependence of the TO response is indistinguishable from the combined temperature-strain dependence of the solid's shear modulus. This implies that the rotational responses of solid helium-4 attributed to supersolidity are associated with generation of the same microscopic excitations as those produced by direct shear strain.