Nonequivalence Of Ensembles Research Articles

Non-equivalence of ensembles in the ground state of a model with annealed bond impurities

We analyze a model, due to Kasai and Syozi, of annealed ferromagnetic bond impurities in an antiferromagnetic host. We show that on all bi-partite lattices the usual grand-canonical approach to treating the average over the impurity configurations leads to a different ground state than the one obtained in the fixed impurity concentration (canonical) ensemble. This difference is caused by a condensation/anti-condensation phenomenon that occurs when the system is in contact with an impurity bath at fixed chemical potential. This phenomenon is illustrated by a complete solution of the model on the Bethe lattice.