Critical properties of generalized four-state clock model on square lattices

We study the finite-temperature transition to the 1/2 magnetization plateau in a model of interacting S = 1/2 spins with longer range interactions and strong exchange anisotropy on the geometrically frustrated Shastry-Sutherland lattice. In previous studies, it was obtained from Monte Carlo calculations that the transition to the plateau state occurs via two successive transitions with the two-dimensional Ising universality class, when the quantum exchange interactions are finite, while a single phase transition takes place in the purely Ising limit[l]. To understand these behaviors, we introduce the generalized four-state chiral clock model and perform Monte Carlo calculations for this model. By comparing the phase diagrams of the two models, we find that the topology of the thermal phase diagram is the same each other - the criticality of the thermal phase transition in the original model can be well explained by that of the generalized four-state chiral clock model.