Nonequivalence of ensembles in the Curie–Weiss anisotropic quantum Heisenberg model
Michael Kästner
The microcanonical entropy s ( e , m ) as a function of the energy e and the magnetization m is computed analytically for the anisotropic quantum Heisenberg model with Curie–Weiss-type interactions. The result shows a number of interesting properties which are peculiar to long-range interacting systems, including nonequivalence of ensembles and partial equivalence. Furthermore, from the shape of the entropy it follows that the Curie–Weiss Heisenberg model is indistinguishable from the Curie–Weiss Ising model in canonical thermodynamics, although they do in general differ in microcanonical thermodynamics. The possibility of experimentally realizing quantum spin models with long-range interactions in a microcanonical setting by means of cold dipolar gases in optical lattices is discussed.
arXiv:1005.5050•Journal of Statistical Mechanics Theory and Experiment•Jul 1, 2010•33 citations