Midgap states ofLa1−xCaxMnO3: Doping-dependent optical-conductivity studies

We investigated the optical-conductivity spectra, σ(ω), of ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ ($x=0.0,$ 0.1, 0.3, 0.5, 0.6, 0.8, 0.9, and 1.0) samples between 5 meV and 30 eV at room temperature. With the hole doping, σ(ω) showed double-peak midgap structures below 3 eV. The lower frequency peak was assigned to an interatomic ${\mathrm{Mn}}^{3+}{\to \mathrm{Mn}}^{4+}$ transition and the higher frequency one was attributed to an intra-atomic transition between Jahn-Teller (JT) split ${\mathrm{Mn}}^{3+}$ levels. This work demonstrated that the local JT effects remained for most samples except ${\mathrm{CaMnO}}_3.$