Ising transition into an order with extensive entropy at T=0: Potts antiferromagnets in a magnetic field

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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 languageEnglish
Pages (from-to)2992-3000
Number of pages9
JournalPhysical Review B
Volume27
Issue number5
DOIs
Publication statusPublished - Jan 1 1983

ASJC Scopus subject areas

  • Condensed Matter Physics

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