Insulator-metal transition in the doped 3d1 transition-metal oxides:
A combined LDA+DMFT study

Luis Craco

Institute of Theoretical Physics, Cologne University, Zuelpicher Str.77, 50937 Cologne, Germany

We analyse the Mott-Hubbard insulator-metal transition (IMT) in 3d1 TM-oxides LaTiO3 and TiOCl using the ab initio LDA+DMFT method. Using the real crystal structure we show that the insulating state is driven by strong multi-orbital correlations with the Mott-Hubbard gap in close agreement with experimental indications. We discuss doping effects away from the d1 limit. Taking into account doping-induced static disorder within the CPA in a self-consistent way along with strong correlations, we obtain very good quantitative agreement with published angle-integrated photoemission results and also quantitatively accurate representation for the unoccupied part of the single particle spectral function of LaTiO3. Further, we discuss an instability of the insulating state to a metallic state by hypothetically adding extra electrons in TiOCl. We find that this metallic state is characterized by a two-fluid picture, and that the IMT should be accompanied by a rapid change in occupation of the various t2g orbitals, characteristic of a multi-orbital Mott-Hubbard transition.