Search for Superfluidity in Solid Hydrogen

TL;DR

This study investigates superfluidity in solid para-hydrogen using torsional oscillator measurements down to 20 mK, finding a phase transition likely caused by residual ortho-hydrogen molecules rather than superfluidity.

Contribution

First experimental search for superfluidity in solid hydrogen using torsional oscillator techniques, revealing a phase transition unrelated to superfluid behavior.

Findings

Observed a phase transition around 60 mK with increased resonant period

Detected extremely long relaxation times linked to residual ortho-hydrogen molecules

Found that period change is not due to superfluidity, unlike in solid helium-4

Abstract

A torsional oscillator study of solid para-hydrogen has been carried out down to 20 mK in search for evidence of superfluidity. This work was inspired by the observation of the supersolid phase in solid He-4. We found evidence of a possible phase transition, marked by an abrupt increase in the resonant period of oscillation and onset of extremely long relaxation times as the temperature was raised above 60 mK. The change in the period for para-hydrogen, in contrast to solid He-4, is not related to superfluidity as it fails a crucial test showing that it is not a consequence of irrotational flow. The long relaxation times observed suggest the effect is related to the motion of residual ortho-hydrogen molecules in the solid.