NMR study of carrier distribution and superconductivity in multilayered high-Tc cuprates

We report Cu-63-Knight shift measurement on multilayered high-T-c cuprate oxides that include inequivalent outer (OP) and inner (IP) CuO2 planes in a unit cell with number of planes n = 3-5. Using an experimental relation between the spin part of Knight shift (K-s) and the carrier concentration (N-h) reported in n = 1 and 2 cuprates, the local carrier concentrations Nh(OP) in the OP and Nh(IP) in the IP have been deduced. We have found that Nh(OP) is larger than Nh(IP) in all the systems. The difference in the doping level increases as total-carrier content delta and n increase. Imbalance between Nh(OP) and Nh(IP) is suggested to be caused by a mechanism that the electrostatic potential associated with the apical oxygen has more attraction for holes in the OP than in the IP. It is also suggested that T-c of Hg 1223 (n = 3) is the highest (T-c = 133 K) to date, due to N-h(IP) optimized to N-h.optimum similar to 0.2 From the fact that N-h(OP)> N-h.optimum, we propose that if Nh(OP) could also be optimized in addition to optimized N-h(IP). T-c might be raised higher than 133 K. (C) 2000 Elsevier Science Ltd. All rights reserved.