Effect of oxygen vacancies on electronic states of ${\mathrm{CaVO}}_{3\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{SrVO}}_{3\mathrm{-}\mathrm{\delta }}$: A photoemission study

There are two structures in the photoemission spectra of ${\mathrm{CaVO}}_{3\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{SrVO}}_{3\mathrm{-}\mathrm{\delta }}$ in the d-band region. One peak is within ∼1 eV of the Fermi level and has a sharp Fermi cutoff. The other is a broad peak centered at ∼1.6 eV. From our photoemission spectra of ${\mathrm{CaVO}}_{3\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{SrVO}}_{3\mathrm{-}\mathrm{\delta }}$ both with oxygen vacancies (δ=∼0.1) and without vacancies (δ=0), it is shown that the relative intensity of the peak near the Fermi level for ${\mathrm{CaVO}}_{3\mathrm{-}\mathrm{\delta }}$ drastically decreases with decreasing oxygen vacancy concentration (δ). In contrast, no such drastic change in intensity is observed for ${\mathrm{SrVO}}_{3\mathrm{-}\mathrm{\delta }}$. This difference in the effect of oxygen vacancies between ${\mathrm{SrVO}}_{3\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{CaVO}}_{3\mathrm{-}\mathrm{\delta }}$ reflects the fact that a metal-insulator phase transition induced by bulk oxygen vacancies takes place in ${\mathrm{CaVO}}_{3\mathrm{-}\mathrm{\delta }}$ but not in ${\mathrm{SrVO}}_{3\mathrm{-}\mathrm{\delta }}$.