Cu NMR Study of Detwinned Single Crystals of Ortho--II YBCO6.5

TL;DR

This study uses copper NMR to analyze oxygen ordering in high-quality Ortho--II YBCO6.5 crystals, revealing detailed local site information and confirming high stoichiometry without static magnetic moments.

Contribution

It provides detailed NMR site assignments and confirms the high stoichiometry and absence of static magnetic moments in detwinned YBCO6.5 crystals.

Findings

Crystals are highly stoichiometric with distinct NMR lines.

No evidence of static magnetic moments was found.

Lower limit on chain length agrees with X-ray data.

Abstract

Copper NMR has been used as a local probe of the oxygen ordering in Ortho--II YBa2Cu3O6.5 crystals grown in BaZrO3 crucibles. Line assignments have been made to each of the expected crystallographically inequivalent sites. The presence of distinct and narrow lines for these sites as well as the lack of a line known to be associated with oxygen defects indicates that these crystals are highly stoichiometric. Our estimate of the lower limit on the chain length is consistent with that derived from X-ray diffraction measurements. In addition, we have found no evidence for static magnetic moments, in contrast to some previous results.