Gap anisotropy and gapless superconductivity in Zn-doped YBa2Cu3O7-δ

Abstract Point-contact spectra of polycrystalline YBa 2 (Cu 1− x Zn x ) 3 O 7 for x =0.05 and 0.075 were studied at various temperatures. Two kinds of point-contact spectra, i.e. differential resistance d V /d I versus voltage V , for the same T c in the point-contact region were found. One type exhibits the well-known features attributed to the energy gap while the features of the other indicate gapless superconductivity. These findings are interpreted in terms of gap ansisotropy with a vanishing gap parallel to the c direction.