Thermal anomalies in molecular hydrogen supercooled in Vycor porous glass

Abstract

We have measured the heat capacity of molecular hydrogen in Vycor porous glass from 6K to 15K using two different methods. The first gives results similar to previous work, with broad peaks corresponding to freezing and melting and at lower temperatures a smooth decrease. The second, which are much closer to thermodynamic equilibrium, resolve three distinct peaks at freezing and reveal a small reproducible anomaly at a lower temperature, not previously observed. Below the anomaly the results fit a roton-type function, and we discuss the possibility that this is consistent with a superfluid state, although our experiments cannot detect it.