Heat Capacities of Submonolayer Solid 3He Films on Graphite at Highly Frustrated Density Regime

The heat capacities (C) of submonolayer solid films adsorbed on a graphite surface are measured down to 100 μK at areal densities between 6.6 and 7.5 nm−2, where there has been no previous measurement below 2 mK. The temperature (T) variation of C shows almost single power low behavior, C ∝ Tα, in a wide temperature range. And the exponent α is much smaller than −2, an expected exponent for localized spins in the high temperature limit. These behaviors should imply that the competition of multiple spin exchange interactions is strong at this density range.