O 1s x‐ray absorption spectroscopy of Tl2Ba2Ca3O10 high‐TC superconductors

X‐ray absorption around oxygen K‐edge of Tl2Ba2Ca2Cu3O10 high‐TC superconductors was measured by means of a bulk sensitive x‐ray fluorescence yield detection method. Three distinct pre‐edge peaks are revealed. They are ascribed to core‐level excitations of oxygen 1s electrons to empty states at Fermi level which have predominantly oxygen 2p character. These oxygen holes are located in CuO2, BaO and TlO planes. The strong dependence of TC on oxygen holes concenration on O(1) site in CuO2 layer is found.