Progress of Theoretical Physics
A Duality between Blocked Ising Models
Y. Kasai
Abstract
For planar lattices, there exists a dual relation between extended (blocked) Ising models in which interactions are expressed by face elements (blocks) instead of bonds. The total interaction for a block contains all even spin products among spins on the face (g-polygon); for g = 2 or 3, it contains only two-spin product, for g = 4 it contains crossed bond interactions and four-spin product, and so on. Formally, there exists a self-dual lattice for every g. The triangular lattice is self-dual for g = 3 and the self-dual lattice for g ≥4 has non integer coordinate number (a rational number) which suggests a universality for the coordination number.