title: Level spectroscopy of the square-lattice three-state Potts model with a ferromagnetic next-nearest-neighbor coupling.
abstract: We study the square-lattice three-state Potts model with the ferromagnetic next-nearest-neighbor coupling at finite temperature. Using the level-spectroscopy method, we numerically analyze the excitation spectrum of the transfer matrices and precisely determine the global phase diagram. Then we find that, contrary to a previous result based on the finite-size scaling, the massless region continues up to the decoupling point with Z3 x Z3 criticality in the antiferromagnetic region. We also check the universal relations among excitation levels to provide the reliability of our result.
authors.affiliation: Department of Physics, Tokyo Metropolitan University, Tokyo 192-0397 Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Otsuka
authors.forename: Koutaro
authors.initials: K
authors.lastname: Mori
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Okabe
authors.forename: Kiyohide
authors.initials: K
authors.lastname: Nomura