title: Ensemble inequivalence in a mean-field XY model with ferromagnetic and nematic couplings.
abstract: We explore ensemble inequivalence in long-range interacting systems by studying an XY model of classical spins with ferromagnetic and nematic coupling. We demonstrate the inequivalence by mapping the microcanonical phase diagram onto the canonical one, and also by doing the inverse mapping. We show that the equilibrium phase diagrams within the two ensembles strongly disagree within the regions of first-order transitions, exhibiting interesting features like temperature jumps. In particular, we discuss the coexistence and forbidden regions of different macroscopic states in both the phase diagrams.
authors.affiliation: Department of Physics and Astronomy, Potsdam University, Karl-Liebknecht-Strasse 24, D-14476 Potsdam, Germany and Department of Control Theory, Nizhni Novgorod State University, Gagarin Avenue 23, 606950 Nizhni Novgorod, Russia.
authors.forename: Arkady
authors.initials: A
authors.lastname: Pikovsky
authors.affiliation: Laboratoire de Physique Théorique et Modèles Statistiques (CNRS UMR 8626), Université Paris-Sud, 91405 Orsay, France.
authors.forename: Shamik
authors.initials: S
authors.lastname: Gupta
authors.affiliation: Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postale 15051, CEP 91501-970 Porto Alegre, Rio Grande do Sul, Brazil.
authors.forename: Tarcisio N
authors.initials: TN
authors.lastname: Teles
authors.affiliation: Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postale 15051, CEP 91501-970 Porto Alegre, Rio Grande do Sul, Brazil.
authors.forename: Fernanda P C
authors.initials: FP
authors.lastname: Benetti
authors.affiliation: Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postale 15051, CEP 91501-970 Porto Alegre, Rio Grande do Sul, Brazil.
authors.forename: Renato
authors.initials: R
authors.lastname: Pakter
authors.affiliation: Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postale 15051, CEP 91501-970 Porto Alegre, Rio Grande do Sul, Brazil.
authors.forename: Yan
authors.initials: Y
authors.lastname: Levin
authors.affiliation: Dipartimento di Fisica e Astronomia and CSDC, Università di Firenze, INFN and CNISM, Via Sansone 1, 50019 Sesto Fiorentino, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Ruffo