Large mass enhancement in ³He monolayer fluids adsorbed on graphite preplated with ⁴He

A fluid monolayer of ³He adsorbed on a graphite surface is an ideal two-dimensional (2D) Fermi system. We have observed very large mass enhancement of the quasiparticles (m*/m = 20 ± 5) in preliminary heat-capacity measurements for high density ³He fluids adsorbed on graphite preplated with a ⁴He monolayer (³He/⁴He/gr). This could be divergence of m* toward the critical density for the 4/7 phase with a triangular lattice, which is a registered phase commensurate against the first layer. The observed m* is larger than those reported for other 2D ³He systems, e.g., m*/m = 13 for ³He/HD/HD/gr system, presumably because of the higher critical density. The apparent divergence of m* toward the different critical densities strongly suggests the Mott-Hubbard type transition between the 2D Fermi fluid phase and the registered phase under a strong onsite hardcore repulsion between the ³He atoms.