Unusual magnetic and superconducting characteristics in multilayered high-T-c cuprates: Cu-63 NMR study - art. no. 064515

We report unusual magnetic and superconducting (SC) characteristics in mult ilayered CuO2 planes in Hg- and Cu-based high-T-c cuprates through the Cu-6 3-NMR measurements. These compounds, in which the number of CuO2 planes (n) ranges from 3 to 5 in a unit cell, include crystallographically inequivale nt outer (OP) and inner (IP) CuO2 plane that are surrounded by pyramidal an d square oxygen, respectively. The Knight shift (K-63) at the OP and IP exh ibits respective characteristic temperature dependence, consistent with its own doping level. Using an experimental relation between the spin part in K-63 at room temperature, and the doping level in a CuO2 layer N-h, we show that N-h,(OP) at the OP is larger than Nh(IP) at the IP for all the system s and its difference DeltaN(h)=N-h(OP) -N-h(IP) increases as either a total carrier content delta or n increases. At DeltaN(h)'s exceeding a critical value, the pseudogap behavior in the normal state is seen alone at the IP. and a bulk SC transition does not set in simultaneously at the IP and OP. A SC nature at the OP becomes consistent with a mean-field behavior only bel ow T-c2 that is significantly lower than T-c. Reduction in T-c with increas ing n is associated with an increase in DeltaN(h). It is a rather remarkabl e aspect that a T-c is not always reduced even though these multilayered hi gh-T-c compounds are heavily overdoped. This arises, we show, because the I P remains underdoped and keeps a high value of T-c, while the OP is predomi nantly overdoped. This may be a microscopic origin for the lowest anisotrop ic SC characteristics reported to date in Cu-based multilayered high-T-c co mpounds.