X-ray spectroscopy ofEuBa2(Cu1−yZny)3O7−x: Suppression of superconductivity

We have studied the x-ray-absorption near-edge spectra of ${\mathrm{EuBa}}_2{{(\mathrm{C}\mathrm{u}}_{1-y}{\mathrm{Zn}}_y)}_3{\mathrm{O}}_7$ as a function of Zn and O content. There is clear evidence for the development of ${\mathrm{Cu}}^{1+}$ ions as the O content is reduced to levels sufficient to suppress superconductivity. However, there is no effect on the electronic state of the Cu ion as the Zn content is increased and superconductivity vanishes. We tentatively conclude that the suppression of superconductivity is in both cases due to the preferred occupancy of certain planes by nonmagnetic (filled $d$ subshell) atoms, as proposed in Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_6$ on the basis of neutron scattering.