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

Abstract We report 63 Cu-Knight shift measurement on multilayered high- T c cuprate oxides that include inequivalent outer (OP) and inner (IP) CuO 2 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 N h (OP) in the OP and N h (IP) in the IP have been deduced. We have found that N h (OP) is larger than N h (IP) in all the systems. The difference in the doping level increases as total-carrier content δ and n increase. Imbalance between N h (OP) and N h (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 Hg1223 ( n =3) is the highest ( T c =133 K) to date, due to N h (IP) optimized to N h,optimum ∼0.2. From the fact that N h (OP)> N h,optimum , we propose that if N h (OP) could also be optimized in addition to optimized N h (IP), T c might be raised higher than 133 K.