Benckiser, E.; Fels, L.; Ghiringhelli, G.; Moretti Sala, M.; Schmitt, T.; Schlappa, J.; Strocov, V.; Mufti, N.; Blake, G.; Nugroho, A.; Palstra, T.; Haverkort, M.; Wohlfeld, K.; Grüninger, M.: Orbital superexchange and crystal field simultaneously at play in YVO3: Resonant inelastic x-ray scattering at the V L edge and the O K edge. Physical Review B 88 (2013), p. 205115/1-13
10.1103/PhysRevB.88.205115

Abstract:
We report on the observation of orbital excitations in YVO3 by means of resonant inelastic x-ray scattering (RIXS) at energies across the vanadium L3 and oxygen K absorption edges. At the V L3 edge, we are able to resolve the full spectrum of orbital excitations up to 5 eV. In order to unravel the effect of superexchange interactions and the crystal field on the orbital excitations, we analyzed the energy and temperature dependence of the intra-t2g excitations at 0.1–0.2 eV in detail. While these results suggest a dominant influence of the crystal field, peak shifts of about 13–20 meV observed as a function of the transferred momentum q∥a reflect a finite dispersion of the orbital excitations. This is puzzling since theoretical models based on superexchange interactions predict a dispersion only for q∥c. Furthermore, we demonstrate that RIXS at the O K edge is very sensitive to intersite excitations. At the O K edge, we observe excitations across the Mott-Hubbard gap and an additional feature at 0.4 eV, which we attribute to two-orbiton scattering, i.e., an exchange of orbitals between adjacent sites. Altogether, our results indicate that both superexchange interactions and the crystal field are important for a quantitative understanding of the orbital excitations in YVO3.