First-Order Transition to Incommensurate Phase with Broken Lattice Rotation Symmetry in Frustrated Heisenberg Model

Abstract

We study a finite-temperature phase transition in the two-dimensional classical Heisenberg model on a triangular lattice with a ferromagnetic nearest-neighbor interaction J 1 and an antiferromagnetic third-nearest-neighbor interaction J 3 using a Monte Carlo method. Apart from a trivial degeneracy corresponding to O(3) spin rotations, the ground state for J 3 ≠0 has a threefold degeneracy corresponding to 120° lattice rotations. We find that this model exhibits a first-order phase transition with the breaking of the threefold symmetry when the interaction ratio is J 3 / J 1 = -3.