英文摘要
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Unoccupied electronic 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 using a bulk-sensitive x-ray-fluorescence-yield technique. 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. As deduced from O K-edge x-ray absorption spectra, the hole concentration in the CuO2 planes of X-Bi2212 increases for X = I and HgI2, but decreases for X = (Py-CH3)2HgI4, relative to pristine Bi2212. The present XANES results clearly demonstrate that the hole density within the CuO2 planes of intercalated Bi2Sr2CaCu2O8 can be not only reduced but also increased, depending on the chemical character of the intercalants.
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