### Abstract

The phase diagram of the q=3 state Potts antiferromagnet in a field is studied by exact mappings and Monte Carlo methods, and it is shown that systems with macroscopic ground-state degeneracy may exhibit conventional-type critical ordering. Our Monte Carlo data for the square-lattice case indicate a finite-temperature ordering in a range of field values where the entropy of the ground state is extensive. In a particular limit this phase transition can be shown to be of the Ising type by mapping the Potts model onto a colored, nearest-neighbor exclusion lattice gas. We also discuss the phase diagram of the body-centered-cubic Ising antiferromagnet in a field in order to show that renormalization-group arguments alone are not sufficient to restrict the diversity of possible low-temperature phases occurring in systems with a macroscopically degenerate ground state.

Original language | English |
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Pages (from-to) | 2992-3000 |

Number of pages | 9 |

Journal | Physical Review B |

Volume | 27 |

Issue number | 5 |

DOIs | |

Publication status | Published - Jan 1 1983 |

### ASJC Scopus subject areas

- Condensed Matter Physics