arXiv:cond-mat/9904218 · Physical Review Letters
Multichain Mean-Field Theory of Quasi-One-Dimensional Quantum Spin Systems
Anders W. Sandvik
Abstract
A multichain mean-field theory is developed and applied to a two-dimensional system of weakly coupled $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$ Heisenberg chains. The environment of a chain ${C}_{0}$ is modeled by a number of neighboring chains ${C}_{\ensuremath{\delta}}$, $\ensuremath{\delta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ifmmode\pm\else\textpm\fi{}1,\dots{},\ifmmode\pm\else\textpm\fi{}n$, with the edge chains ${C}_{\ifmmode\pm\else\textpm\fi{}n}$ 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 are compared with simulation results for the original Hamiltonian on large rectangular lattices. Both methods show that the staggered magnetization $M$ for small interchain couplings $\ensuremath{\alpha}$ behaves as $M\ensuremath{\sim}\sqrt{\ensuremath{\alpha}}$ enhanced by a multiplicative logarithmic correction.