Orbital Fluctuations in the Different Phases ofLaVO3andYVO3

We investigate the importance of quantum orbital fluctuations in the orthorhombic and monoclinic phases of the Mott insulators LaVO(3) and YVO(3). First, we construct ab initio material-specific t(2g) Hubbard models. Then, by using dynamical mean-field theory, we calculate the spectral matrix as a function of temperature. Our Hubbard bands and Mott gaps are in very good agreement with spectroscopy. We show that in orthorhombic LaVO(3), quantum orbital fluctuations are strong and that they are suppressed only in the monoclinic 140 K phase. In YVO(3)the suppression happens already at 300 K. We show that Jahn-Teller and GdFeO3-type distortions are both crucial in determining the type of orbital and magnetic order in the low temperature phases.