Anomalous heat capacities in submonolayer solid 3He films commensurate to graphite substrate

The heat capacities (C) of submonolayer solid 3He films adsorbed on a graphite surface are measured down to 100 μK at areal densities between 6.6 and 7.5 nm−2, where 3He film is expected to be commensurate to the corrugation of the adsorption potential of the graphite substrate and some novel adsorption structures have been predicted. In this areal density regime there has been no previous measurement below 2 mK. The temperature (T) variation of C shows almost single power law 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.