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

We report Cu-63-Knight shift measurement on multilayered high-T-c cuprate o xides 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 bet ween 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 le vel increases as total-carrier content delta and n increase. Imbalance betw een Nh(OP) and Nh(IP) is suggested to be caused by a mechanism that the ele ctrostatic 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 122 3 (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 pro pose 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. Al l rights reserved.