Defect fugacity, spin-wave stiffness and of the 2d planar rotor model

¹ Institut für Physik, Johannes Gutenberg Universität Mainz - 55099, Mainz, Germany
² Universität Konstanz, Fakultät für Physik, Fach M 691 - 78457, Konstanz, Germany

Received: 24 January 2000
Accepted: 5 April 2000

Abstract

We obtain precise values for the fugacities of vortices in the 2d planar rotor model from Monte Carlo simulations in the sector with no vortices. The bare spin-wave stiffness is also calculated and shown to have significant anharmonicity. Using these as inputs in the KT recursion relations, we predict the temperature , using linearised equations, and using next higher-order corrections, at which vortex unbinding commences in the unconstrained system. The latter value, being in excellent agreement with all recent determinations of , demonstrates that our method 1) constitutes a stringent measure of the relevance of higher-order terms in KT theory and 2) can be used to obtain transition temperatures in similar systems with modest computational effort.