We have studied the electronic nature of the layered oxysulfide Sr2-x Cax Cu2 CoO2 S2 which has strongly correlated CoO2 square planes. These materials exhibit narrow-gap semiconducting behavior and the conduction mechanism depends on the temperature. Valence band x-ray photoemission spectroscopy spectra show that Ca doping and the production of Sr defects cause the generation of a quasiparticle band near the Fermi level. These phenomena suggest that the materials are changing from correlated semiconductors to bad metals.
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