SPECIFIC-HEAT OF QUANTUM HEISENBERG-MODEL ON A TRIANGULAR LATTICE WITH 2 EXCHANGE PARAMETERS AND ITS APPLICATION TO HE-3 ADSORBED ON GRAPHITE

The quantum Heisenberg model on a triangular lattice with two exchange parameters, J between nearest-neighbor spins forming a Kagome net, and eta-J between spins in the Kagome net and ones at the center of each unit cell of the Kagome net, is studied using the Wigner-Jordan transformation. The specific heat calculated from the model is found to have a double-peak structure when eta is finite but substantially smaller than 1. The experimentally measured specific heat of the second-layer HE-3 adsorbed on graphite can be explained in terms of our model calculation.