Possibility of d-wave superconductivity in high-Tc superconductor - NMR study in YBa 2(Cu 1−xM x) 3O 7 ( M= Zu, Ni) -

Abstract

The superconducting property of YBa 2(Cu 1−xM x) 3O 7 ( M= Zn, Ni) has been investigated by 63Cu NQR and NMR tenchniques. In case of Zn(ed 10) doped into CuO 2, the residual spin knight shift of 63Cu increases appreciably with increasing concentration. Correspondingly, T 1T=const. law holds far below T c, providing a signature of the gapless superconductivity. The behavior of rapid decrease of 1/T 1 just below T c has commonly been observed as in most of the high-T c materials. These results are well interpreted by a combined effect of the gap zeros of lines at the Fermi surface originating from a d-wave pairing and the residual density of states at the Fermi level induced by non-magnetic Zn-impurities 1). In contrast, there is no clear sign of the gapless superconductivity caused by Ni(3d 8) impurities, although we point out that the undoped system itself posseses more or less a gapless feature induced by some imperfection of the crystal.