Doping variation of orbitally-induced anisotropy in electronic structure of the perovskite-type vanadium oxides

Recently, the perovskite-type vanadium oxide LaVO$_{3}$ has been attracting much attention. In this system, the anisotropic charge dynamics due to the one-dimensional orbital exchange interaction is observed. In addttion, the filling control insulator-metal transition (FC-IMT) concomitant with the orbital ordering-disordering transition can be achieved in the hole doped system La$_{1-x}$Sr$_{x}$VO$_{3}$[1]. In this study, the variation of anisotropic charge dynamics in the course of FC-IMT in the perovskite-type vanadium oxide has been investigated by measurements of optical conductivity spectra with focus on the role of t$_{2g}$-orbital degree of freedom. The orbitally-induced anisotropic feature of the Mott-gap excitation as well as of the doping-induced mid-infrared excitation is suppressed with increasing the hole concentration, and instead the isotropic and incoherent dynamics of the doped hole dominates over the low-energy excitation near and above the IMT point. \newline \newline [1] S.Miyasaka et al., Phys.Rev.Lett. 85,5388(2000)