Physical review. B, Condensed matter
Critical properties of a general class of Z(5)-symmetric spin models
B. Bonnier, K. Rouidi
Abstract
We study the isotropic, ferromagnetic two-dimensional spin systems with Z(5) symmetry, which, in the general case, depend upon two couplings, a temperature and a parameter \ensuremath{\Omega}, used to interpolate continuously between the clock (\ensuremath{\Omega}=0) and the Potts (\ensuremath{\Omega}=1) models, passing through the integrable Fateev-Zamolodchikov case (\ensuremath{\Omega}=${\mathrm{\ensuremath{\Omega}}}_{\mathit{c}}$\ensuremath{\approxeq}0.618). Two methods, the high-temperature expansion and the exact \ensuremath{\beta} function on finite lattices, are applied within the Hamiltonian formulation to study critical properties. The transitions found are first order (${\mathrm{\ensuremath{\Omega}}}_{\mathit{c}}$\ensuremath{\le}1), second order of the Ising type (\ensuremath{\Omega}\ensuremath{\simeq}${\mathrm{\ensuremath{\Omega}}}_{\mathit{c}}$), or of the Kosterlitz-Thouless type (0\ensuremath{\le}\ensuremath{\Omega}${\mathrm{\ensuremath{\Omega}}}_{\mathit{c}}$) with a varying exponent.