Impact of Oxygen Diffusion on Superconductivity in YBa$_2$Cu$_3$O$_{7-\delta}$ Thin Films Studied by Positron Annihilation Spectroscopy

TL;DR

This study investigates how oxygen diffusion affects superconductivity in YBa₂Cu₃O₇−δ thin films using positron annihilation spectroscopy, revealing depth-dependent oxygen profiles and critical temperatures.

Contribution

It introduces in situ Doppler broadening spectroscopy to analyze oxygen diffusion and its impact on superconductivity in YBCO films, providing new insights into depth-dependent oxygen profiles.

Findings

Oxygen diffusion causes depth-dependent δ in YBCO films.

Steady-state oxygen exchange occurs within minutes at surface and interface.

Depth-dependent critical temperature T_c is observed in the films.

Abstract

The oxygen deficiency $\delta$ in YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) plays a crucial role for affecting high-temperature superconductivity. We applied (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 SrTiO$_3$ (STO) substrates. The oxygen diffusion during tempering was 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 revealed the depth dependent critical temperature $T_{\mathrm{c}}$ in the as prepared and tempered YBCO film.