Temperature and Spin Dependent Correlation Length of the Quantum Heisenberg Antiferromagnet on the Square Lattice

The quantum Heisenberg antiferromagnet (HAF) is approached by the pure-quantum self-consistent harmonic approximation that reduces it to an effective classical HAF model. The effective exchange, weakened by quantum fluctuations, enters the classical-like expression for thermal averages as a temperature scale, so that one can obtain in a simple way the quantum spin correlation length from its classical counterpart. For any spin value S the results compare very well with those from experiments, quantum Monte Carlo simulations, and high-T expansion. The adequacy of our theory and supports arguments previously raised against the quantitative validity of the mapping of the quantum HAF onto the quantum nonlinear sigma model. copyright 1996 The American Physical Society