Direct observation of Pr-CuO₂ hybridization in PrBa₂Cu₃O_7-δ by the MEM charge density study

In order to prove the existence of hybridization between the Pr and CuO₂ conduction planes, a charge density study of PrBa₂Cu₃O_6.87(PrBCO) and YBa₂Cu₃O_6.97(YBCO) has been carried out by the maximum entropy method (MEM) using synchrotron radiation (SR) powder data. In the charge density of PrBCO obtained by MEM, there can be found directional robes of the charge density from the Pr atom toward the O atoms in the CuO₂-planes. For YBCO there have not been observed appreciable charge densities in the interatomic region around the Y atom. The distinct difference of the charge densities between PrBCO and YBCO presents clear experimental evidence of the hybridization between Pr 4f-O 2p_π orbitals which supports the idea that the hole trapping by the hybridized states suppresses the superconductivity in PrBCO.