Effects of ring exchange interaction on the Neel phase of two-dimensional, spatially anisotropic, frustrated Heisenberg quantum antiferromagnet

摘要

Higher order quantum effects on the magnetic phase diagram induced byfour-spin ring exchange on plaquettes are investigated for a two-dimensionalquantum antiferromagnet with S=1/2. Spatial anisotropy and frustration areallowed for. Using a perturbative spin-wave expansion up to second order in 1/Swe obtain the spin-wave energy dispersion, sublattice magnetization, and themagnetic phase diagram. We find that for substantial four-spin ring exchangethe quantum fluctuations are stronger than in the standard Heisenberg model. Amoderate amount of four-spin ring exchange couplings stabilizes the orderedantiferromagnetic Neel state while a large amount renders it unstable.Comparison with inelastic neutron scattering data points toward a moderate ringexchange coupling of 27% to 29% of the nearest-neighbor exchange coupling.