Dynamics of coupled quantum spin chains

Static and dynamical properties of weakly coupled antiferromagnetic spin chains are treated using a mean--field approximation for the interchain coupling and exact results for the resulting effective one--dimensional problem. Results for staggered magnetization, N\'eel temperature and spin wave excitations are in agreement with experiments on $\rm KCuF_3$. The existence of a narrow longitudinal mode is predicted. The results are in agreement with general scaling arguments, contrary to spin wave theory.Comment: 12 pages, 1 figure, RevTeX 3.0, uuencoded file, some refs adde

Weakly Coupled Antiferromagnetic Quantum Spin Chains

Quasi-one-dimensional quantum antiferromagnets formed by a d-dimensional hypercubic lattice of weakly coupled spin-1/2 antiferromagnetic Heisenberg chains are studied by combining exact results in one-dimension and renormalization group analyses of the interchain correlations. It is shown that d-dimensional magnetic long-range order develops at zero-temperature for infinitesimal antiferromagnetic or ferromagnetic interchain couplings. In the presence of weak bond alternations, the order-disorder transition occurs at a finite interchain coupling. Relevances to the lightly doped quantum antiferromagnets and multi-layer quantum Hall systems are discussed.Comment: 12 revtex pages, no figures, revised final version to appear in PR