NMR and NQR studies of superconductivity in heavily doped Tl 2Ba 2CuO 6+y with a single CuO 2 plane

Abstract

The superconducting property of Tl 2Ba 2CuO 6+y (TBCO) with T c =72, 40 and 0 K has been investigated by 63Cu NQR and NMR and 205Tl NMR measurements. The behaviors of the Knight shift and nuclear spin lattice relaxation time T 1 below T c have been found to be almost the same as those in YBA 2Cu 3O 7, although the behavior above T c is strongly modified in the sense that the q-dependence of the abtiferromagnetic (AF) spin fluctuation becomes less distinct upon doping. According to the argument for YBCO 7 by Ishida et al., the T-dependence of 1 T 1 and the Knight shift below T c in TBCO are well interpreted by a “gapless d-wave model” with a finite density of states at the Fermi surface. It is pointed out that impurities and imperfections and/or the applied magnetic field more or less cause the pair breaking in TBCO. Then the low- T properties in high- T c oxides are concluded to be seriously affected by the small but finite density of states at the Fermi depending on the material.