Absence of supersolidity in solid helium in porous Vycor glass

TL;DR

This study investigates whether solid helium in porous Vycor glass exhibits supersolidity by conducting a shear modulus stiffening-free torsional oscillator experiment, finding no evidence of nonclassical rotational inertia.

Contribution

The paper presents a novel experimental design that eliminates shear modulus effects, conclusively showing the absence of supersolidity in helium confined in Vycor.

Findings

No measurable period drop attributed to NCRI was observed.

Shear modulus stiffening does not account for period drops in this setup.

Results challenge previous claims of supersolidity in confined helium.

Abstract

In 2004, Kim and Chan (KC) carried out torsional oscillator (TO) measurements of solid helium confined in porous Vycor glass and found an abrupt drop in the resonant period below 200 mK. The period drop was interpreted as probable experimental evidence of nonclassical rotational inertia (NCRI). This experiment sparked considerable activities in the studies of superfluidity in solid helium. More recent ultrasound and TO studies, however, found evidence that shear modulus stiffening is responsible for at least a fraction of the period drop found in bulk solid helium samples. The experimental configuration of KC makes it unavoidable to have a small amount of bulk solid inside the torsion cell containing the Vycor disc. We report here the results of a new helium in Vycor experiment with a design that is completely free from any bulk solid shear modulus stiffening effect. We found no measureable period drop that can be attributed to NCRI.