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Ensemble inequivalence in a mean-field XY model with ferromagnetic and nematic couplings
Arkady Pikovsky1, Shamik Gupta2, Tarcisio N Teles3
1Department 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.
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.
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