Low Temperature Heat-Capacities of Liquid ³He Thin Films

Abstract

We have measured the heat capacity of ³ He thin films adsorbed on graphite at an areal density of 15.0 nm ⁻² down to as low as 100 μK. The second-layer ³ He behaves as a degenerate 2D Fermi fluid in the whole temperature range we studied. We observed no anomalous behavior in the heat capacity near 3 mK in contradiction to the recent report by other workers. This indicates that possible superfluid transitions would be below 100 μK. Instead, a small and temperature-independent contribution to the heat capacity was observed, which we attribute to nuclear-spin degrees of freedom in glassy solid ³ He trapped in substrate heterogeneities.