Momentum dependence of orbital excitations in Mott-insulating titanates

TL;DR

This study uses high-resolution resonant inelastic x-ray scattering to investigate the momentum dependence of orbital excitations in Mott-insulating titanates, comparing experimental data with theoretical models.

Contribution

It demonstrates that a superexchange model with two-orbiton excitations best explains the observed orbital excitation modes.

Findings

Superexchange model fits experimental data well.

Orbital excitations show clear momentum dependence.

Two-orbiton excitations are key to understanding the data.

Abstract

High-resolution resonant inelastic x-ray scattering has been used to determine the momentum dependence of orbital excitations in Mott-insulating LaTiO$_3$ and YTiO$_3$ over a wide range of the Brillouin zone. The data are compared to calculations in the framework of lattice-driven and superexchange-driven orbital ordering models. A superexchange model in which the experimentally observed modes are attributed to two-orbiton excitations yields the best description of the data.