Optical spectra of ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{VO}}_3$: Change of electronic structures with hole doping in Mott-Hubbard insulators

In perovskitelike solid solutions ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ca}}_{\mathit{x}}$ ${\mathrm{VO}}_3$, the insulator-metal transition has been observed around x=0.5, which can be interpreted as being caused by hole doping in a Mott-Hubbard insulator ${\mathrm{YVO}}_3$. Change of electronic structures has been investigated by measurements and analyses of optical spectra. New electronic states were observed to grow within the Mott-Hubbard gap upon hole doping and eventually compose the states near the Fermi level in the metallic phase. Doping-induced changes of electronic structures are argued in comparison with the case of cuprate superconductors.