Probing orbital fluctuations in RVO 3 (R = Y, Gd, or Ce) by ellipsometry

We study optical excitations across the Mott gap in the multiorbital Mott-Hubbard insulators RVO ₃. The multipeak structure observed in the optical conductivity can be described consistently in terms of the different 3d3 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 that orbital fluctuations are strong in RVO ₃. Both the line shape and the temperature dependence give clear evidence for the importance of excitonic effects.