Spin Correlation Functions in the Large-α Region of the Square-Lattice J1–J2Model

Abstract

In the context of modified spin–wave theory, we perform a finite-temperature spin–wave calculation in the large-α region of the J 1 –J 2 model, where α= J 2 / J 1 . 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 J 1 –J 2 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 \(\sqrt{2}a\). 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.