MONTE-CARLO SIMULATION OF THE HEISENBERG-ANTIFERROMAGNET ON A TRIANGULAR LATTICE - TOPOLOGICAL EXCITATIONS

We have simulated the classical Heisenberg antiferromagnet on a triangular lattice using a local Monte Carlo algorithm. The behavior of the correlation length xi, the susceptibility at the ordering wave vector chi(Q), and the spin stiffness rho clearly reflects the existence of two temperature regimes-a high-temperature regime T > T-th, in which the disordering effect of vortices is dominant, and a low-temperature regime T < T-th, where correlations are controlled by small amplitude spin fluctuations. As has previously been shown, in the last regime, the behavior of the above quantities agrees well with the predictions of a renormalization-group treatment of the appropriate nonlinear sigma model. For T > T-th, a satisfactory fit of the data is achieved, if the temperature dependence of xi and chi(Q) is assumed to be of the form predicted by the Kosterlitz-Thouless theory. Surprisingly, the crossover between the two regimes appears to happen in a very narrow temperature interval around T-th similar or equal to 0.28.