Determination of electronic band structures ofCaMnO3andLaMnO3using optical-conductivity analyses

Reflectivity spectra of ${\mathrm{CaMnO}}_3$ and ${\mathrm{LaMnO}}_3$ were measured in a wide photon energy region between 5 meV and 30 eV at room temperature. Using the conductivity spectra obtained from the Kramers-Kronig analysis, electronic structures of the manganese oxides were investigated. In particular, the states near the Fermi energy ${\mathrm{E}}_{\mathrm{F}}$, O 2p and Mn 3d (${\mathrm{e}}_{\mathrm{g}}$,${\mathrm{t}}_{2\mathrm{g}}$), were studied in detail. It was found that the O 2p band is located closer to ${\mathrm{E}}_{\mathrm{F}}$ than the Mn ${\mathrm{t}}_{2\mathrm{g}}$ band. For ${\mathrm{LaMnO}}_3$, the filled Mn ${\mathrm{e}}_{\mathrm{g}\mathrm{\uparrow }}^1$ band is located closer to ${\mathrm{E}}_{\mathrm{F}}$ than any other valence band. The ${\mathrm{t}}_{2\mathrm{g}}$-${\mathrm{e}}_{\mathrm{g}}$ Hund exchange energy was found to be about 3.4 eV and the Jahn-Teller stabilization energy ${\mathrm{E}}_0$ was estimated to be less than 0.5 eV.