Influence of Ortho-H2 Clusters on the Mechanical Properties of Solid Para-H2

TL;DR

This study investigates how ortho-H2 impurity clusters influence the elastic and mechanical properties of solid para-H2, revealing impurity dynamics impact resonant oscillation behavior without indicating a supersolid transition.

Contribution

It provides new insights into impurity clustering effects on solid para-H2's elastic response using torsional oscillator experiments and finite element modeling.

Findings

Impurity clustering affects the resonant period of oscillation.

The period change is linked to elastic response alterations, not supersolidity.

An abrupt period increase above 100 mK is due to impurity-dislocation interactions.

Abstract

The quantum diffusion of ortho-H2 impurities in solid para-H2 has been investigated with a torsional oscillator technique. The unclustering dynamics of agglomerated impurities with increasing temperature are found to greatly affect the resonant period of oscillation. Based on the observed trends in both experimental data and complementary finite element calculations, we find that the oscillation period predominantly reflects changes in the solid's elastic response to the minute inertial stresses imposed on it. It is likely that the small but abrupt increase in the resonant period observed above 100 mK in high purity H2 samples is due to the interplay between remnant ortho-H2 impurities and dislocations, and not a signature of a supersolid to normal solid transition.