We report a coexistence of superconductivity and antiferromagnetism in five-layered compound HgBa2Ca4Cu5Oy (Hg-1245) with Tc = 108 K, which is composed of two types of CuO2 planes in a unit cell; three inner planes (IP's) and two outer planes (OP's). The Cu-NMR study has revealed that the optimallydoped OP undergoes a superconducting (SC) transition at Tc = 108 K, whereas the three underdoped IP's do an antiferromagnetic (AF) transition below TN ∼ 60 K with the Cu moments of ∼ (0.3 − 0.4)µB . Thus bulk superconductivity with a high value of Tc = 108 K and a static AF ordering at TN = 60 K are realized in the alternating AF and SC layers. The AF-spin polarization at the IP is found to induce the Cu moments of ∼ 0.02µB at the SC OP, which is the AF proximity effect into the SC OP.

We report unusual magnetic and superconducting ͑SC͒ characteristics in multilayered CuO 2 planes in Hgand Cu-based high-T c cuprates through the 63 Cu-NMR measurements. These compounds, in which the number of CuO 2 planes ͑n͒ ranges from 3 to 5 in a unit cell, include crystallographically inequivalent outer ͑OP͒ and inner ͑IP͒ CuO 2 plane that are surrounded by pyramidal and square oxygen, respectively. The Knight shift ( 63 K) 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 63 K at room temperature and the doping level in a CuO 2 layer N h , we show that N h (OP) at the OP is larger than N h (IP) at the IP for all the systems and its difference ⌬N h ϭN h (OP)ϪN h (IP) increases as either a total carrier content ␦ or n increases. At ⌬N 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 below T c2 that is significantly lower than T c . Reduction in T c with increasing n is associated with an increase in ⌬N h . It is a rather remarkable aspect that a T c is not always reduced even though these multilayered high-T c compounds are heavily overdoped. This arises, we show, because the IP remains underdoped and keeps a high value of T c , 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-T c compounds.

No abstract

No abstract

No abstract