Modified spin-wave theory of a square-lattice antiferromagnet

Abstract

A modified spin-wave theory for the Heisenberg antiferromagnet (scrH=J) is formulated under the assumption of zero sublattice magnetization in the same way with the Heisenberg ferromagnet. This theory gives self-consistent equations which are equivalent to those of Auerbach and Arovas, but in our theory the factor of (3/2 in the correlation function does not appear. This theory reproduces the main results of traditional spin-wave theory, as well as those of renormalization-group theory, in a unified picture. For the square lattice at low temperature the susceptibility behaves as a+bT and the correlation length as (c/T)exp(d/T). This correlation length coincides very well with experimental results of ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$ if we choose J=900 K. Calculation of self-consistent equations is done for the S=(1/2 system and compared with the result of exact diagonalization of a 4×4 system and high-temperature expansion. The quantitative agreement is surprisingly good, especially at T≲0.6J. .AE