Abstract
We study the square lattice Heisenberg antiferromagnet with spatially anisotropic nearest-neighbor couplings and frustrated by a next-nearest-neighbor coupling numerically using the density-matrix renormalization-group (DMRG) method and analytically employing the Schwinger-Boson mean-field theory (SBMFT). Up to relatively strong values of the anisotropy, within both methods we find quantum fluctuations to stabilize the Néel-ordered state above the classically stable region. Whereas SBMFT suggests a fluctuation-induced first-order transition between the Néel state and a stripe antiferromagnet for and an intermediate paramagnetic region opening only for very strong anisotropy, the DMRG results clearly demonstrate that the two magnetically ordered phases are separated by a quantum-disordered region for all values of the anisotropy with the remarkable implication that the quantum paramagnetic phase of the spatially isotropic model is continuously connected to the limit of decoupled Haldane spin chains. Our findings indicate that for quantum fluctuations in strongly frustrated antiferromagnets are crucial and not correctly treated on the semiclassical level.
3 More- Received 20 January 2009
DOI:https://doi.org/10.1103/PhysRevB.79.174409
©2009 American Physical Society