OXYGEN K NEAR-EDGE X-RAY-ABSORPTION SPECTROSCOPY OF LA2-XMXCUO4 (M=CA, SR AND BA) - X-DEPENDENCE OF HOLE STATE DENSITY

Fluorescence-yield oxygen K near-edge X-ray spectroscopy was utilized as a bulk-sensitive method to determine the hole state density of La2- xMxCuO4. Pre-edge features have been measured for M=Sr, 0 less-than-or -equal-to x less-than-or-equal-to 0.40, M=Ba, 0 less-than-or-equal-to x less-than-or-equal-to 0.25, and M=Ca, 0 less-than-or-equal-to x less -than-or-equal-to 0.10. These features occur just above the Fermi leve l at approximately 530 and approximately 528 eV, the 528 eV peak being assigned to holes in the oxygen 2p band. The intensities and energies of these peaks were determined as a function of composition x. Result s are qualitatively similar among M=Sr, Ba and Ca. For x less-than-or- equal-to 0.15 the magnitude of the 528 eV peak is linear in x. In the overdoped region, x>0.15, M=Sr, the magnitude begins to saturate.