The spin-wave spectrum of the Jahn-Teller system LaTiO3

TL;DR

This paper analytically calculates the spin-wave spectrum of LaTiO3, including all relevant superexchange interactions, and finds results consistent with experimental neutron and Raman data.

Contribution

It provides a comprehensive analytical model of the spin-wave spectrum of LaTiO3, incorporating all symmetry-allowed superexchange couplings, which was not previously achieved.

Findings

Calculated four-branch spin-wave dispersion with small zone-center gaps

Lower-energy modes agree with neutron-scattering experiments

Predicted higher-energy branches match Raman data

Abstract

We present an analytical calculation of the spin-wave spectrum of the Jahn-Teller system LaTiO3. The calculation includes all superexchange couplings between nearest-neighbor Ti ions allowed by the space-group symmetries: The isotropic Heisenberg couplings and the antisymmetric (Dzyaloshinskii-Moriya) and symmetric anisotropies. The calculated spin-wave dispersion has four branches, two nearly degenerate branches with small zone-center gaps and two practically indistinguishable high-energy branches having large zone-center gaps. The two lower-energy modes are found to be in satisfying agreement with neutron-scattering experiments. In particular, the experimentally detected approximate isotropy in the Brillouin zone and the small zone-center gap are well reproduced by the calculations. The higher-energy branches have not been detected yet by neutron scattering but their zone-center gaps are in satisfying agreement with recent Raman data.