Electron spectroscopic investigation of the semiconductor-metal transition in La_1−xSr_xMnO₃

Abstract

We study the electronic structure of La_1−xSr_xMnO_3+δ , 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 E_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 E_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 LaMnO₃, 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 U_dd=4.0 eV, suggesting a mixed character for the ground state of LaMnO₃.