Possible twin-boundary effect upon the properties of high-T_{c} superconductors

Abstract

We have studied the field at which superconductivity nucleates in grain-aligned samples of ${\mathrm{Y}}_1$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ very close to the transition temperature $T_c$. For the field parallel to the c axis and for temperatures within 2 K of $T_c$, the nucleation field is found to vary as (1-T/$T_c$ ${)}^{1/2}$. The data suggest that superconductivity localized near twin boundaries may exist at temperatures close to $T_c$. .AE