Non-Classical Response from Quench-Cooled Solid Helium Confined in Porous Gold

TL;DR

This study investigates the non-classical rotational inertia in quench-cooled solid helium confined in porous gold, revealing growth-rate dependent decoupling and relaxation phenomena suggestive of complex low-energy excitations.

Contribution

It provides new insights into how quench-cooling and pore confinement influence non-classical responses in solid helium, highlighting the role of low-energy excitations and their pinning.

Findings

Nearly 7% decoupling observed in rapidly grown solid helium below 200 mK

Decoupling is reduced in slowly grown solid helium

Extended relaxation indicates pinning of low-energy excitations

Abstract

We have investigated the non-classical response of solid 4He confined in porous gold set to torsional oscillation. When solid helium is grown rapidly, nearly 7% of the solid helium appears to be decoupled from the oscillation below about 200 mK. Dissipation appears at temperatures where the decoupling shows maximum variation. In contrast, the decoupling is substantially reduced in slowly grown solid helium. The dynamic response of solid helium was also studied by imposing a sudden increase in the amplitude of oscillation. Extended relaxation in the resonant period shift, suggesting the emergence of the pinning of low energy excitations, was observed below the onset temperature of the non-classical response. The motion of a dislocation or a glassy solid is restricted in the entangled narrow pores and is not likely responsible for the period shift and long relaxation.