Spin Correlation Functions in the Large-α Region of the Square-Lattice J₁–J₂ Model

Abstract

In the context of modified spin–wave theory, we perform a finite-temperature spin–wave calculation in the large-α region of the J₁–J₂ model, where α=J₂⁄J₁. The spin correlation functions for large separations are calculated and the correlation lengths at very low temperatures are given. The two-types of spin correlation functions with a spatial anisotropy are obtained, and each of them is expressed in terms of the two different correlation lengths. At α→∞, the J₁–J₂ model on the square lattice with a lattice spacing a should physically be divided into the two disconnected square-lattice antiferromagnets with a lattice spacing \\sqrt2a. At this limit, one of our two correlation functions vanishes and the other is correctly reduced to the one in the square-lattice antiferromagnet. Also the two correlation lengths are unified and are reduced to the one in the above square-lattice antiferromagnet.