Positron annihilation in the high-temperature superconductor YBa2Cu3O6+ delta.

Abstract

Positron-annihilation lifetime and Doppler broadening energy spectra have been measured in high-temperature superconductors $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+\ensuremath{\delta}}$ as a function of temperature between 10 and 293 K. The observed positron lifetime and Doppler boradening $S$ parameter show an onset increase near the superconducting critical temperature (${T}_{c}=90$ K). This variation does not exist in a similar nonsuperconducting sample that contains a saturated oxygen vacancy content. These results give evidence that the oxygen vacancy and electronic structure change play an important role for high-${T}_{c}$ superconductivity.