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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.

We report a careful 59Co nuclear quadrupolar resonance measurement on the recently discovered cobalt oxyhydrate Na0.35CoO2.yH(2)O superconductor from T=40 K down to 0.2 K. We find that in the normal state the spin-lattice relaxation rate 1/T(1) follows a Curie-Weiss type temperature (T) variation, 1/T(1)T=C/(T-theta), with theta=-42 K, suggesting two-dimensional antiferromagnetic spin correlations. Below T(c)=3.9 K, 1/T(1) decreases with no coherence peak and follows a T(n) dependence with n approximately 2.2 down to approximately 2.0 K but crosses over to a 1/T(1) proportional to T variation below T=1.4 K, which suggests non-s-wave superconductivity. The data in the superconducting state are most consistent with the existence of line nodes in the gap function.

We report measurements of the 115 In nuclear spin-lattice relaxation rate (1/T1) between T =0.09 K and 100 K in the new heavy fermion (HF) compound CeIrIn5. At 0.4 K ≤ T ≤ 100 K, 1/T1 is strongly T -dependent, which indicates that CeIrIn5 is much more itinerant than known Ce-based HFs. We find that 1/T1T , subtracting that for LaIrIn5, follows a ( 1 T +θ ) 3 4 variation with θ=8 K. We argue that this novel feature points to anisotropic, due to a layered crystal structure, spin fluctuations near a magnetic ordering. The bulk superconductivity sets in at 0.40 K below which the coherence peak is absent and 1/T1 follows a T 3 variation, which suggests unconventional superconductivity with line-node gap. PACS: 74.25.Ha, 74.70Tx, 76.60.Gv The emergence of superconductivity near a magnetic instability in cerium (Ce)-based heavy fermion (HF) compounds is one of the most intriguing phenomena in strongly correlated electron systems. Except for CeCu 2 Si 2 which is superconducting at ambient pressure with T c =0. . In spite of efforts and progress, however, knowledge about this class of superconductors is still limited because of difficult experimental conditions. The recently discovered new family of Ce-based heavy electron systems, CeMIn 5 (M=Rh, Ir) with M=Ir being a superconductor already at ambient pressure [6,7], provides new opportunities for studying the nature of the superconductivity in the vicinity of a magnetic instability, the interplay between magnetic excitations and superconductivity, etc. In particular, CeIrIn 5 is suitable for studies using microscopic experimental probes that can be applied more easily at ambient pressure.CeMIn 5 (M=Rh, Ir) consists of alternating layers of CeIn 3 and MIn 2 . CeRhIn 5 is an antiferromagnet with T N =3.8 K but becomes superconducting below T c =2.1 K under pressures larger than 1.6 GPa [6]. In CeIrIn 5 , the resistivity is already zero at ambient pressure below 1.2 K, but the Meissner effect and the jump in the specific heat are found only at 0.4 K [7]. The electronic specific heat coefficient γ is found to be 750 mJ/mol K 2 [7], which suggests a large mass enhancement. Recent de Haas-van Alphen Oscillation in CeIrIn 5 also reveals a cyclotron mass that is ∼20 times larger than the band mass, consistent with the specific heat result [8].In this Letter, we report a measurement using local probe, the 115 In nuclear quadrupolar resonance (NQR) study in CeIrIn 5 down to 90 mK, at zero magnetic field.From the temperature (T ) dependence of the nuclear spin lattice relaxation rate (1/T 1 ), we find that CeIrIn 5 is much more itinerant than known Ce-compounds such as CeCu 2 Si 2 [9], and show that this compound is located near a magnetic ordering with anisotropic spin fluctuations due to the layered crystal structure. No anomaly was found at 1.2 K in the NQR quantities, but 1/T 1 shows an abrupt decrease at 0.40 K below which the NQR intensity also decreases as does the ac susceptibility, confirming a bulk superconductivity below T c =0.40 K. The lack of coherence peak in 1/T...

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We report Sb-NQR results which evidence a heavy-fermion (HF) behavior and an unconventional superconducting (SC) property in Pr(Os4Sb12 with T(c)=1.85 K. The temperature (T) dependence of nuclear-spin-lattice-relaxation rate, 1/T(1), and NQR frequency unravel a low-lying crystal-electric-field splitting below T0 approximately 10 K, associated with Pr3+(4f(2))-derived ground state. In the SC state, 1/T(1) shows neither a coherence peak just below T(c) K nor a T3-like power-law behavior observed for anisotropic HF superconductors with the line-node gap. The isotropic energy gap with its size Delta/k(B)=4.8 K seems to open up across T(c) below T(*) approximately 2.3 K. It is surprising that Pr(Os4Sb12 looks like an isotropic HF superconductor-it may indeed argue for Cooper pairing via quadrupolar fluctuations.

We report 115 In nuclear-quadrupole-resonance ͑NQR͒ measurements of the pressure( P)-induced superconductor CeRhIn 5 in the antiferromagnetic ͑AF͒ and superconducting ͑SC͒ states. In the AF region, the internal field H int at the In site is substantially reduced from H int ϭ1.75 kOe at Pϭ0 to 0.39 kOe at Pϭ1.23 GPa, while the Néel temperature slightly changes with increasing P. This suggests that either the size in the ordered moment M Q ( P) or the angle ( P) between the direction of M Q ( P) and the tetragonal c axis is extrapolated to zero at P*ϭ1.6Ϯ0.1 GPa at which a bulk SC transition is no longer emergent. In the SC state at P ϭ2.1 GPa, the nuclear spin-lattice relaxation rate 115 (1/T 1 ) has revealed a T 3 dependence without the coherence peak just below T c , giving evidence for the unconventional superconductivity. The dimensionality of the magnetic fluctuations in the normal state is also discussed.