Abstract
The role of twin boundaries and impurities in the superconducting properties of twinned and detwinned single crystals of YBa 2Cu 3O 7−δ is studied via magnetically modulated microwave absorption (MAMMA) and SQUID magnetometry. Twin boundaries do not affect the T c (91.5 K) or the width of the superconducting transition of high quality gold-doped samples. In contrast, a twinned crystal containing additional impurities exhibits a lower T c (88 K), a larger transition width, and a secondary transition ( T c = 86 K) due most likely to the segregation of impurities at the twin boundaries. A 10–15% anisotropy in the value of d T c/d H is observed in the a-b plane of the detwinned crystal.
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