Phase Transitions of Anisotropic Heisenberg Antiferromagnets on the Triangular Lattice

Abstract

Phase transitions in anisotropic Heisenberg antiferromagnets with nearest neighbour coupling constants (J_x, J_y, J_z) on the triangular lattice have been investigated. In particular, for the case of Heisenberg-Ising model, |J_z|>|J_x|=|J_y|>0, successive phase transitions due to orderings of z components and of xy components have been found. A non-trivial degeneracy is found both in the ground state and in harmonic excitations. Divergent-like behaviour of the uniform susceptibility in the xy plane at low temperatures is found, which is supposed to be caused by the non-trivial degeneracy.