Oscillation Frequency Dependence of Non-Classical Rotation Inertia of Solid $^4$He

TL;DR

This study investigates how the oscillation frequency affects the non-classical rotational inertia of solid helium-4 at ultra-low temperatures, revealing mode-dependent behavior linked to critical velocity rather than amplitude.

Contribution

It demonstrates the frequency dependence of non-classical rotational inertia in solid helium-4 and identifies critical velocity as the key factor influencing the phenomenon.

Findings

Non-classical rotational inertia fraction is consistent below 35 mK at low velocities.

Above 35 mK, higher frequency modes show greater inertia fraction.

Reduction in inertia is governed by critical velocity, not amplitude or acceleration.

Abstract

The non-classical rotational inertia fraction of the identical cylindrical solid $^4$He below 300 mK is studied at 496 and 1173 Hz by a double resonance torsional oscillator. Below 35 mK, the fraction is the same at sufficiently low rim velocities. Above 35 mK, the fraction is greater for the higher than the lower mode. The dissipation peak of the lower mode occurs at a temperature $\sim$ 4 mK lower than that of the higher mode. The drive dependence of the two modes shows that the reduction of the fraction is characterized by critical velocity, \textit{not} amplitude nor acceleration.