Weak universality, bicritical points and reentrant transitions in the critical behaviour of a mixed spin-1/2 and spin-3/2 Ising model on the union jack (centered square) lattice

TL;DR

This paper analyzes the critical behavior of a mixed spin-1/2 and spin-3/2 Ising model on the union jack lattice, revealing exact solutions, universality classes, and bicritical phenomena through mappings to the eight-vertex model.

Contribution

It establishes an exact solution for the model via mappings to the eight-vertex model, exploring universality, bicritical points, and reentrant transitions.

Findings

Critical points follow the Ising universality class.

Existence of bicritical points with interaction-dependent exponents.

Reentrant phase transitions observed in the model.

Abstract

The mixed spin-1/2 and spin-3/2 Ising model on the union jack lattice is solved by establishing a mapping correspondence with the eight-vertex model. It is shown that the model under investigation becomes exactly soluble as a free-fermion eight-vertex model 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. This surface is bounded by a line of bicritical points having interaction-dependent critical exponents that satisfy a weak universality hypothesis.