Peculiar hole doping by Ca substitution in cuprate superconductors

Abstract

The doping effect of Ca substitution in Y0.7Ca0.3Ba2Cu3Oy has been studied for y=6.9 and 6 by the x-ray absorption near edge spectroscopy (XANES). While Ca doping leads to an obvious increase in hole concentration in the CuO2 planes in Y0.7Ca0.3Ba2Cu3O6.9, XANES indicates absence of this doping effect in Y0.7Ca6.3Ba2Cu3O6. These two contradict results suggest that the doping effect by Ca substitution could be sensitive to the oxygen content when y similar to6.0. Comparisons with others' works are made.