Search for Superfluidity in Solid Hydrogen

Abstract

A torsional oscillator study of solid para-hydrogen has been carried out down to 20 mK in a search for evidence of superfluidity. 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. In contrast to solid 4He, the change in the period for para-hydrogen is not a consequence of irrotational superflow. The long relaxation times observed suggest the effect is related to the motion of residual ortho-hydrogen molecules in the solid.

Enhanced superfluid response of parahydrogen in nanoscale confinement

“…It was first suggested in 1972 that a fluid of p-H 2 molecules should undergo a superfluid transition at a temperature close to 6 K [1]. However, the observation of this hypothetical superfluid has so far been prevented by the simple fact that, unlike helium, p-H 2 solidifies [2] at a temperature of 13.8 K, under the pressure of its own vapor. This is due to the depth of the attractive well of the interaction between two p-H 2 molecules, about three times greater than that between two helium atoms, imparting to the system a strong propensity to crystallize, even in reduced dimensions [3].…”

Supersolid Phases of Cold Atom Assemblies

“…Albeit effects due to Bose statistics are detectable in the momentum distribution of liquid parahydrogen near freezing [15], in general the behavior of condensed molecular hydrogen is much closer to that of a classical system than to helium. Indeed, while some theoretical [16,17] and experimental [18] evidence of superfluidity (and even possible supersolidity [19]) in small clusters of parahydrogen (comprising around twenty molecules) has been reported, agreement is virtually unanimous that bulk condensed parahydrogen displays no superfluid behavior [20,21].…”

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

“…Although the low temperature feature appears to be of similar nature to that in solid 4 He experiments [7], it is not due to the onset of superfluidity [16]. overall behavior was the same for all samples in three different TOs and for all concentrations in the range studied, ∼5×10 −3 < x < 0.025.…”

“…3a. All samples were grown and measured in the TO from [16]. Since we are interested in changes to τ following an increase in temperature, constant offsets have been subtracted from each trace such that they all coincide at 0 K. The temperature dependence of the relative period shift ∆τ between 150 mK and 1 K is approximately linear for the empty cell, HD sample, and x = 0.15 H 2 sample.…”