Unusual magnetic and superconducting characteristics in multilayered high-Tc cuprates: 63Cu NMR study

Abstract

We report unusual magnetic and superconducting (SC) characteristics in multilayered CuO2 planes in Hg- and Cu-based high-Tc cuprates through the 63Cu−NMR measurements. These compounds, in which the number of CuO2 planes (n) ranges from 3 to 5 in a unit cell, include crystallographically inequivalent outer (OP) and inner (IP) CuO2 plane that are surrounded by pyramidal and square oxygen, respectively. The Knight shift (63K) at the OP and IP exhibits respective characteristic temperature dependence, consistent with its own doping level. Using an experimental relation between the spin part in 63K at room temperature and the doping level in a CuO2 layer Nh, we show that Nh(OP) at the OP is larger than Nh(IP) at the IP for all the systems and its difference ΔNh=Nh(OP)−Nh(IP) increases as either a total carrier content δ or n increases. At ΔNh’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 below Tc2 that is significantly lower than Tc. Reduction in Tc with increasing n is associated with an increase in ΔNh. It is a rather remarkable aspect that a Tc is not always reduced even though these multilayered high-Tc compounds are heavily overdoped. This arises, we show, because the IP remains underdoped and keeps a high value of Tc, while the OP is predominantly overdoped. This may be a microscopic origin for the lowest anisotropic SC characteristics reported to date in Cu-based multilayered high-Tc compounds.

Source-reported materials — not catalogue approval

Similar papers