Probing orbital fluctuations in RVO3 (R = Y, Gd, or Ce) by ellipsometry

TL;DR

This study investigates optical excitations in RVO3 Mott insulators, revealing the significance of excitonic effects and the impact of spin and orbital correlations on spectral features, challenging the orbital fluctuation scenario.

Contribution

It provides experimental evidence against strong orbital fluctuations in RVO3 and highlights the role of excitonic effects in optical spectra.

Findings

Spectral weight depends on temperature and polarization.

Comparison rules out strong orbital fluctuations.

Evidence supports excitonic effects in optical excitations.

Abstract

We study optical excitations across the Mott gap in the multi-orbital Mott-Hubbard insulators RVO3. The multi-peak structure observed in the optical conductivity can be described consistently in terms of the different 3d^3 multiplets or upper Hubbard bands. The spectral weight is very sensitive to nearest-neighbor spin-spin and orbital-orbital correlations and thus shows a pronounced dependence on both temperature and polarization. Comparison with theoretical predictions based on either rigid orbital order or strong orbital fluctuations clearly rules out the latter. Both, the line shape and the temperature dependence give clear evidence for the importance of excitonic effects.