Multiboson spin-wave theory for Ba2CoGe2O7, a spin-3/2 easy-plane Neel antiferromagnet with strong single-ion anisotropy

TL;DR

This paper develops a multiboson spin-wave theory for Ba2CoGe2O7, a spin-3/2 antiferromagnet with strong single-ion anisotropy, successfully explaining experimental neutron scattering spectra and predicting new spin stretching modes.

Contribution

It introduces a novel multiboson spin-wave approach for spin-3/2 systems with strong anisotropy, extending understanding of their excitation spectra.

Findings

Reproduces experimental neutron scattering spectra accurately.

Predicts the emergence of spin stretching modes at 4 meV.

Suggests spin stretching modes are common in S>1/2 systems with strong anisotropy.

Abstract

We consider the square-lattice antiferromagnetic Heisenberg Hamiltonian extended with a single-ion axial anisotropy term as a minimal model for the multiferroic Ba2CoGe2O7. Developing a multiboson spin-wave theory, we investigate the dispersion of the spin excitations in this spin-3/2 system. As a consequence of a strong single-ion anisotropy, a stretching (longitudinal) spin-mode appears in the spectrum. The inelastic neutron scattering spectra of Zheludev et al. [Phys. Rev. B 68, 024428 (2003)] are successfully reproduced by the low energy modes in the multiboson spin-wave theory, and we anticipate the appearance of the spin stretching modes at 4meV that can be identified using the calculated dynamical spin structure factors. We expect the appearance of spin stretching modes for any S>1/2 compound where the single-ion anisotropy is significant.