EXPERIMENTAL HOLE DENSITIES IN HGBA2CAN-1CUNO2N-EDGE X-RAY-ABSORPTIONSPECTROSCOPY(2+DELTA COMPOUNDS FROM NEAR)

Near-edge x-ray-absorption spectroscopy measurements have been perform ed on the O K'- and Cu L-absorption edges on a series of underdoped an d optimally doped HgBa2Can-1CunO2n+2+delta samples in order to get qua ntitative information on the changes in the electronic structure under doping with excess O. The density of doped holes with O 2p character per CuO2 plane per unit cell in the optimized samples is found to be c lose to that of other p-type doped superconducting cuprates with optim ized T-c. There is also some evidence for a decreasing density of thes es doping-induced O 2p hole states per CuO2 plane per unit cell with i ncreasing number n of CuO2 sheets for the samples with optimized T-c. Finally, a quantitative analysis of the experimental data leads to dop ing levels in the Hg systems that are half of what is expected in a si mple ionic picture.