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

TL;DR

This study explores how four-spin ring exchange interactions influence the magnetic phases of a two-dimensional, frustrated quantum antiferromagnet, revealing that moderate ring exchange stabilizes the Neel order while large amounts destabilize it.

Contribution

It provides a perturbative spin-wave analysis of the effects of ring exchange on the phase diagram, including quantum fluctuations and stability of the Neel state.

Findings

Moderate ring exchange stabilizes the Neel phase.

Large ring exchange destabilizes the antiferromagnetic order.

Comparison with neutron scattering suggests 27-29% ring exchange coupling.

Abstract

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