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Models with short- and long-range interactions: the phase diagram and the reentrant phase

par Dauxois, T.;de Buyl, Pierre ;Lori, Leonardo;Ruffo, Stefano
Référence Journal of Statistical Mechanics: Theory and Experiment, 2010, 6, page (P06015)
Publication Publié, 2010-06-15

Article révisé par les pairs

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Résumé :

We study the phase diagram of two different Hamiltonians with competing local, nearest-neighbour, and mean-field couplings. The first example corresponds to the HMF Hamiltonian with an additional short-range interaction. The second example is a reduced Hamiltonian for dipolar layered spin structures, with a new feature with respect to the first example: the presence of anisotropies. The two examples are solved in both the canonical and the microcanonical ensemble using a combination of the min–max method with the transfer operator method. The phase diagrams present typical features of systems with long-range interactions: ensemble inequivalence, negative specific heat and temperature jumps. Moreover, for a given range of parameters, we report the signature of phase reentrance. This can also be interpreted as the presence of azeotropy with the creation of two first-order phase transitions with ensemble inequivalence, as one parameter is varied continuously.