Cu/Tl-NMR study on the impurity effect for Tl-based high- Tc cuprate in the over-doped region

Abstract

The non-magnetic impurity effect has been investigated by NMR on Zn-doped TlBa 2CaCu 2O 7 + δ belonging to the over-doped region, where the reduction rate in T c with Zn-doping was found to be approximately −2.3 K/%, much smaller than La 1.85Sr 0.15CuO 4 and YBa 2Cu 3O 7. The temperature dependence of the Cu-NMR Knight shift was analyzed with the partially closed d-wave model proposed by Ishida et al. to find that the residual density of states at the Fermi level increases with the Zn-concentration. The ratio between the residual density of states and the reduction rate in T c was found to be in accordance with the theoretical calculation in the unitarity limit by Miyake.