Structures of 3He adsorbed on graphite

The second layer of He-3 adsorbed on graphite solidifies when its density is nearly 4/7 of that of the first layer. The registered phase on the triangular lattice formed by the first layer of He-3 was proposed by Elser for this solid phase. In order to clarify this solid phase, we have examined the Hubbard model on the triangular lattice within mean field approximation. We have used the simulated annealing method for finite lattices with 4/7 filling. Changing strength of the on-site interaction and the periodic boundary conditions(7 x 7, 7 x 6 and 7 x 5), we have obtained the most stable particle density structures with magnetic orderings. The results show that there are non-uniform particle density orderings at moderately large strength of the on-site interaction. These non-uniform particle orderings can be considered as the candidates for the solid phase of the second layer of He-3. (C) 1998 Elsevier Science B.V. All rights reserved.