EVIDENCE FOR O-2P HOLE-DRIVEN CONDUCTIVITY IN LA1-XSRXMNO3 LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.7) AND LA0.7SR0.3MNOZ THIN-FILMS

Oxygen K-edge electron-energy-loss spectra have been measured for La1- xSrxMnO3 (0 less than or equal to x less than or equal to 0.7) and La0 .7Sr0.3MnOz thin films as a function of x and z. The spectra show a pr epeak 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 thro ugh divalent doping (x) or oxygen content (z). This confirms that thes e materials are charge-transfer-type oxides with carriers having signi ficant oxygen 2p hole character. We argue that, the double exchange me chanism has to include the role of oxygen hole density to satisfactori ly describe their transport properties.