Hubbard exciton revealed by time-domain optical spectroscopy
  We use broadband ultra-fast pump-probe spectroscopy in the visible range to study the lowest excitations across the Mott-Hubbard gap in the orbitally ordered insulator YVO3. Separating thermal and non-thermal contributions to the optical transients, we show that the total spectral weight of the two lowest peaks is conserved, demonstrating that both excitations correspond to the same multiplet. The pump-induced transfer of spectral weight between the two peaks reveals that the low-energy one is a Hubbard exciton, i.e. a resonance or bound state between a doublon and a holon. Finally, we speculate that the pump-driven spin-disorder can be used to quantify the kinetic energy gain of the excitons in the ferromagnetic phase. 
Fabio Novelli, Daniele Fausti, Julia Reul, Federico Cilento, P. H. M.   van Loosdrecht, A. A. Nugroho, T. T. M. Palstra, Mar...
cond-mat.str-el