Electron spectroscopic investigation of the semiconductor-metal transition in ${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{MnO}}_3$

We study the electronic structure of ${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{MnO}}_{3+\mathrm{\delta }}$, x=0, 0.1, 0.2, 0.3, and 0.4, across the semiconductor-metal transition, using various electron spectroscopy techniques. The negligible intensity seen at ${\mathit{E}}_{\mathit{F}}$ using ultraviolet photoemission spectroscopy and bremsstrahlung isochromat spectroscopy (BIS) indicate an unusual semiconductor-metal transition observed for x≥0.2, consistent with the resistivity data. The BIS spectra show doped hole states developing about 1.4 eV above ${\mathit{E}}_{\mathit{F}}$ as a function of x. Auger electron spectroscopy gives an estimate of the intra-atomic Coulomb energy in the O 2p manifold to be about 6.8 eV. The Mn 2p core-level spectrum of ${\mathrm{LaMnO}}_3$, analyzed in terms of a configuration-interaction calculation, gives parameter values of the charge-transfer energy Δ=5.0 eV, the hybridization strength between Mn 3d and O 2p states, t=3.8 eV, and the on-site Coulomb energy in Mn 3d states ${\mathit{U}}_{\mathit{d}\mathit{d}}$=4.0 eV, suggesting a mixed character for the ground state of ${\mathrm{LaMnO}}_3$.