Detection and imaging of the oxygen deficiency in single crystalline YBa$_{\text{2}}$Cu$_{\text{3}}$O$_{\text{7}-\delta}$ thin films using a positron beam

TL;DR

This study uses a mono-energetic positron beam to detect and image oxygen deficiency in single crystalline YBCO thin films, revealing a linear correlation with the critical temperature and spatial variations within the films.

Contribution

It introduces a novel positron beam technique for quantifying and imaging oxygen deficiency in YBCO thin films, supported by ab-initio calculations to validate the method.

Findings

Linear correlation between Doppler broadening and oxygen deficiency δ

Spatial fluctuations of δ within single YBCO films up to 0.079(5)

Positron probing remains effective despite potential vacancies

Abstract

Single crystalline YBa$_{\text{2}}$Cu$_{\text{3}}$O$_{\text{7}-\delta}$ (YBCO) thin films were grown by pulsed laser deposition (PLD) in order to probe the oxygen deficiency $\delta$ using a mono-energetic positron beam. The sample set covered a large range of $\delta$ (0.191<$\delta$<0.791) yielding a variation of the critical temperature $T_{\text{c}}$ between 25 and 90\,K. We found a linear correlation between the Doppler broadening of the positron electron annihilation line and $\delta$ determined by X-ray diffraction (XRD). Both, the origin of the found correlation and the influence of metallic vacancies, were examined with the aid of ab-initio calculations that allowed us (i) to exclude the presence of Y vacancies and (ii) to ensure that positrons still probe $\delta$ despite the potential presence of Ba or Cu vacancies. In addition, by scanning with the positron beam the spatial variation of $\delta$ could be analyzed. It was found to fluctuate with a standard deviation of up to $0.079(5)$ within a single YBCO film.