Very Low-Temperature Specific Heat of Submonolayer Helium Films

Abstract

The specific heats of ${\mathrm{He}}^3$ and ${\mathrm{He}}^4$ films adsorbed on exfoliated graphite have been measured between 0.04 and 4.2 K, for fractional monolayer coverages between 0.25 and 0.63. ${\mathrm{He}}^3$ films show anomalies around 0.1 K that are absent in the ${\mathrm{He}}^4$ results. A possible explanation is given in terms of spin ordering of the ${\mathrm{He}}^3$ atoms.