Heat capacity of multilayers of He3 adsorbed on graphite at low millikelvin temperatures

作者：Dennis S. Greywall · 发表于：Physical review. B, Condensed matter · 年份：1990 · DOI：10.1103/physrevb.41.1842 · 被引用次数：274 · 研究领域：Quantum, superfluid, helium dynamics、Physics of Superconductivity and Magnetism、Advanced Condensed Matter Physics

Precise heat-capacity results are presented for $^{3}\mathrm{He}$ adsorbed on graphite. The temperature range of the data is from 2 to 200 mK, while the coverages span from somewhat below monolayer completion up through five atomic layers. Promotion of atoms into the second, third, and fourth layers is clearly observed. Nuclear-spin exchange energies of the order of a few tenths of a mK are found for the submonolayer incommensurate solid phase. These values differ significantly from those recently inferred from NMR experiments. Data for the second-layer fluid yield $^{3}\mathrm{He}$ quasiparticle effective masses that agree well with the corresponding first-layer values and range from one to five times the bare $^{3}\mathrm{He}$ mass. Prior to third-layer promotion, the second layer undergoes a first-order phase transition. By comparison with the phase diagram for the first layer, the new phase in the second layer is assumed to be a registered solid. Registry is now with respect to the first $^{3}\mathrm{He}$ layer, which continues to exist as a triangular-lattice solid incommensurate with the graphite substrate. The registered phase exhibits a large, sharp heat-capacity anomaly at 2.5 mK.This anomaly may be due to antiferromagnetic polarons which form around zero-point vacancies or may be the signature of an unusual registered phase in which some of the atoms are positioned at substrate potential maxima. As the coverage is increased further, the second-layer spin peak remain...