Hole states of X-Bi2Sr2CaCu2O8 [X=I, HgI2, and (Py-CH3)2HgI4] probed by O K-edge X-ray absorption spectroscopy

Hole states of X-Bi2Sr2CaCu2O8 [X-Bi2212, X=I, HgI2, and (Py-CH3)2-HgI4, Py = pyridine] have been probed by O K-edge X-ray absorption near-edge structure (XANES) spectra. In the O 1s absorption edge of X-Bi2212, the pre-edge peak at ∼528.3 eV is attributed to transitions into the O 2p hole states located in the CuO2 planes. The hole concentration in the CuO2 planes of X-Bi2212 increases for X=I and HgI2, but decreases for X= (Py-CH3)2HgI4 as coMPared to pristine Bi2212. The variation of CuO2-plane hole concentration of Bi2212 is primarily responsible for the Tc variation upon intercalation.