Ensemble inequivalence in the Blume-Emery-Griffiths model near a fourth-order critical point.

Prasad, V V; Campa, Alessandro; Mukamel, David; Ruffo, Stefano · Phys Rev E · 2019

basic_science · Level V

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Abstract

The canonical phase diagram of the Blume-Emery-Griffiths model with infinite-range interactions is known to exhibit a fourth-order critical point at some negative value of the biquadratic interaction K<0. Here we study the microcanonical phase diagram of this model for K<0, extending previous studies which were restricted to positive K. A fourth-order critical point is found to exist at coupling parameters which are different from those of the canonical ensemble. The microcanonical phase diagram of the model close to the fourth-order critical point is studied in detail revealing some distinct features from the canonical counterpart.