Experimental evidence for fast cluster formation of chain oxygen vacancies in YBa2Cu3O7-d being at the origin of the fishtail anomaly

TL;DR

This study provides experimental evidence that clustering of oxygen vacancies in YBa2Cu3O7-d causes the fishtail anomaly, highlighting the importance of defect organization in superconducting properties.

Contribution

It demonstrates that oxygen vacancy clusters, not single vacancies, are responsible for the fishtail anomaly in YBa2Cu3O7-d, using multiple experimental techniques.

Findings

Oxygen vacancy clusters correlate with the fishtail anomaly.

Single vacancies do not cause the anomaly.

Optimal doping suppresses the anomaly.

Abstract

We report on three different and complementary measurements, namely magnetisation measurements, positron annihilation spectroscopy and NMR measurements, which give evidence that the formation of oxygen vacancy clusters is on the origin of the fishtail anomaly in YBa2Cu3O7-d. While in the case of YBa2Cu3O7.0 the anomaly is intrinsically absent, it can be suppressed in the optimally doped state where vacancies are present. We therefore conclude that the single vacancies or point defects can not be responsible for this anomaly but that clusters of oxygen vacancies are on its origin.