Classical and quantum anisotropic Heisenberg antiferromagnets

Selke, W., Bannasch, G., Holtschneider, M., McCulloch, I.P., Peters, D., and Wessel, S.
Institut für Theoretische Physik and JARA-SIM, Technische Hochschule Aachen, Aachen, Germany;
Department of Physics, University of Queensland, Brisbane, Australia
Institut für Theoretische Physik, Universität Stuttgart, Stuttgart, Germany


We study classical and quantum Heisenberg antiferromagnets with exchange anisotropy of XXZ--type and crystal field single--ion terms of quadratic and cubic form in a field. The magnets display a variety of phases, including the spin--flop (or, in the quantum case, spin--liquid) and biconical (corresponding, in the quantum lattice gas description, to supersolid) phases. Applying ground--state considerations, Monte Carlo and density matrix renormalization group methods, the impact of quantum effects and lattice dimension is analysed. Interesting critical and multicritical behaviour may occur at quantum and thermal phase transitions