Termination of the Berezinskii-Kosterlitz-Thouless phase with a new critical universality in spin-crossover systems

Abstract

Two dimensional systems with U(1) symmetry exhibit a peculiar phase, i.e., the Berezinskii-Kosterlitz-Thouless (BKT) phase. In particular situations, the BKT phase exists as an intermediate temperature phase. There have been scenarios for the phase transitions at the two endpoints of the intermediate BKT phase, i.e., the phase transition at the low-temperature endpoint is a BKT transition and that at the high-temperature endpoint is either a BKT transition or a first-order transition. The present study gives a novel scenario, i.e., a second-order transition with a new critical universality and a BKT transition. We found that this new phase transition is realized in spin-crossover systems on a triangular lattice with an antiferromagnetic short-range interaction. At the low-temperature transition the elastic interaction plays as a ferromagnetic infinite-range interaction and encourages the breaking of $Z_2$ symmetry between high-spin rich and low-spin rich states.

18 pages, 7 figures

References in corpus (2)

• Simple Two-Dimensional Model for the Elastic Origin of Cooperativity among Spin States of Spin-Crossover Complexes
• Realization of the mean-field universality class in spin-crossover materials

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• Nontrivial phase diagram for an elastic interaction model of spin crossover materials with antiferromagnetic-like short-range interactions
• Multistability in an unusual phase diagram induced by the competition between antiferromagnetic-like short-range and ferromagnetic-like long-range interactions
• Multiple Coulomb phases with temperature tunable ice rules in pyrochlore spin crossover materials
• Spin-state smectics in spin crossover materials