Annealing in solid $^4$He

TL;DR

This study confirms the nonclassical rotational inertia in solid helium-4 using a torsional oscillator and investigates how annealing affects dissipation and NCRI signals at high pressure.

Contribution

It presents new experimental results on the effects of annealing in solid helium-4, highlighting changes in dissipation and NCRI signals at constant temperatures above 1 K.

Findings

NCRI confirmed with torsional oscillator measurements.

Strong correlation between NCRI and high dissipation.

Annealing causes a rise in period and a decay in dissipation.

Abstract

We have used a torsional oscillator with square cross section and a resonance frequency of 185 Hz to confirm the nonclassical rotational inertia (NCRI) discovered by Kim and Chan\cite{1,2}. We have also found a strong correlation between the NCRI signal and a high dissipation Q$^{-1}$ of 4 $\times$ 10$^{-6}$ of the oscillation above the transition temperature. Here, we present preliminary results of the annealing process in $^{4}$He at a pressure of 26 bar. When holding the temperature constant above 1 K we have observed a immediate rise in the period and a slow decay of the dissipation. The equilibrium value of Q$^{-1}$ decreases with increasing temperature.