Evidence for O_2p hole-driven conductivity in La_1−xSr_xMnO₃ (0 ≤ x ≤ 0.7) and La_0.7Sr_0.3MnO_z thin films

Oxygen K-edge electron-energy-loss spectra have been measured for La_1−xSr_xMnO₃ (0 ≤ x ≤ 0.7) and La_0.7Sr_0.3MnO_z thin films as a function of x and z. The spectra show a prepeak at the Fermi level, corresponding to transitions to empty states in the O_2p band, at the threshold of the K edge around 529 eV. This prepeak systematically increases with an increase in conductivity through divalent doping (x) or oxygen content (z). This confirms that these materials are charge-transfer-type oxides with carriers having significant oxygen 2p hole character. We argue that, the double exchange mechanism has to include the role of oxygen hole density to satisfactorily describe their transport properties.