Dresden 2006 – wissenschaftliches Programm

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DY: Dynamik und Statistische Physik

DY 46: Poster

DY 46.124: Poster

Donnerstag, 30. März 2006, 16:00–18:00, P1

Weak universality, bicritical points and reentrant transitions of the mixed-spin Ising model on the union jack lattice — •Lucia Canova, Jan Dely, and Jozef Strecka — Department of Theoretical Physics and Astrophysics, Faculty of Science, P. J. Safarik University, 040 01 Kosice, Slovakia

The mixed spin-1/2 and spin-S (S>1/2) Ising model on the union jack (centered square) lattice is solved by establishing a mapping correspondence with the uniform eight-vertex model by following the procedure worked out previously by Lipowski and Horiguchi [1]. It is shown that the model under investigation becomes exactly soluble as a free-fermion eight-vertex model [2] when the parameter of uniaxial single-ion anisotropy tends to infinity. Under this restriction, the critical points are characterized by critical exponents from the standard Ising universality class. In a certain subspace of interaction parameters, which corresponds to a coexistence surface between two ordered phases, the model becomes exactly soluble as a symmetric zero-field eight-vertex model [3]. This surface is bounded by a line of bicritical points, which have interaction-dependent critical exponents that satisfy a weak universality hypothesis [4]. In the rest of the parameter space, the free-fermion approximation [2] is used in order to estimate the criticality of the model system.

[1] A. Lipowski, T. Horiguchi, J. Phys. A: Math. Gen. 28 (1995) L261.

[2] C. Fan and F. Y. Wu, Phys. Rev. B 2 (1970) 723.

[3] R. J.Baxter, Exactly solved models in statistical mechanics

(Academic Press, New York, 1982).

[4] M. Suzuki, Progr. Theor. Phys. 51 (1974) 1992