The oxygen deficiency $\delta$ in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ (YBCO) plays a crucial role for affecting high-temperature superconductivity. We apply (coincident) Doppler broadening spectroscopy of the electron-positron annihilation line to study in situ the temperature dependence of the oxygen concentration and its depth profile in single crystalline YBCO film grown on ${\mathrm{SrTiO}}_3$ (STO) substrates. The oxygen diffusion during tempering is found to lead to a distinct depth dependence of $\delta$, which is not accessible using x-ray diffraction. A steady state reached within a few minutes is defined by both, the oxygen exchange at the surface and at the interface to the STO substrate. Moreover, we reveal the depth-dependent critical temperature $T_{\mathrm{c}}$ in the as prepared and tempered YBCO film.

• Received 12 February 2018

DOI:https://doi.org/10.1103/PhysRevB.97.144503