Multichain mean-field theory of quasi-one-dimensional quantum spin systems

A multichain mean-field theory is developed and applied to a two-dimensiona l system of weakly coupled S = 1/2 Heisenberg chains. The environment of a chain C-0 is modeled by a number of neighboring chains C-delta, delta = +/- 1,..., +/-n, with the edge chains C+/-n coupled to a staggered field. Using a quantum Monte Carlo method, the effective (2n + 1)-chain Hamiltonian is solved self-consistently for n UP to 4. The results an compared with simula tion results for the original Hamiltonian on large rectangular lattices. Bo th methods show that the staggered magnetization M for small interchain cou plings alpha behaves as M similar to root alpha enhanced by a multiplicativ e logarithmic correction.