Quantum Degeneracy and Phase Separation in Solid Two-DimensionalHe3-He4Mixture Films Adsorbed on Graphite

The effects of quantum degeneracy due to the tunneling motion of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ atoms in a two-dimensional solid isotopic solution have been observed through measurements of the nuclear magnetic susceptibility. This system constitutes a solid phase with the features of a heavy fermion fluid. A phase transition, identified as isotopic phase separation, was observed directly through the time variation of the magnetic susceptibility. The critical temperature was 50 mK with a time constant for phase separation of order 5 h at 10 mK.