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 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.

We report a study on the interplay between antiferromagnetism (AFM) and superconductivity (SC) in a heavy-fermion compound CeRhIn5 under pressure P=1.75 GPa. The onset of the magnetic order is evidenced from a clear split of 115In nuclear quadrupole resonance spectrum due to the spontaneous internal field below the Néel temperature T(N)=2.5 K. Simultaneously, bulk SC below T(c)=2.0 K is demonstrated by the observation of the Meissner diamagnetism signal whose size is the same as in the exclusively superconducting phase. These results indicate that the AFM coexists homogeneously with the SC at a microscopic level.

We report In-NQR and Co-NMR experiments of CeCoIn5 that undergoes a superconducting transition with a record high Tc = 2.3 K to date among heavy-fermion superconductors. At zero magnetic field, an anomalous temperature (T ) dependence of nuclear spin-lattice relaxation rate 1/T1 of 115 In is explained by the relation 1/T1 ∝ T · χQ(T ) 3/4 based on the anisotropic spinfluctuations model in case of the proximity to an antiferromagnetic (AFM) quantum critical point (QCP). The novel behavior of 1/T1 ∼ T 1/4 over a wide T range of Tc < T < 40 K arises because the staggered susceptibility almost follows the Curie law χQ(T ) ∝ 1/(T + θ) with θ = 0.6 K and hence 1/T1 ∝ T /(T + 0.6) 3/4 ∼ T 1/4 for θ < T . We highlight that the behavior 1/T1 ∼ T 1/4 is due to the proximity to the anisotropic AFM QCP relevant with its layered structure, and is not associated with the AFM QCP for isotropic 3D systems. We have also found that the AFM spin fluctuations in CeCoIn5 are suppressed by small magnetic field so that θ = 0.6 K at H=0 increases to θ = 2.5 K at H = 1.1 T, reinforcing that CeCoIn5 is closely located at the QCP.

We report the discovery of new superconducting and novel magnetic phases in CeIn3 on the verge of antiferromagnetism (AFM) under pressure (P ) through the In-nuclear quadrupole resonance (NQR) measurements. We have found a P -induced phase separation of AFM and paramagnetism (PM) without any trace for a quantum phase transition in CeIn3. A new type of superconductivity (SC) was found in P = 2.28 − 2.5 GPa to coexist with AFM that is magnetically separated from PM where the heavy fermion SC takes place. We propose that the magnetic excitations such as spindensity fluctuations induced by the first-order magnetic phase transition might mediate attractive interaction to form Cooper pairs.

We report the novel pressure(P ) -temperature(T ) phase diagram of antiferromagnetism and superconductivity in CeRhIn5 and CeIn3 revealed by the 115 In nuclear-spin-lattice-relaxation (T1) measurement. In the itinerant magnet CeRhIn5, we found that the Néel temperature TN is reduced at P ≥ 1.23 GPa with an emergent pseudogap behavior. In CeIn3, the localized magnetic character is robust against the application of pressure up to P ∼ 1.9 GPa, beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges. We discuss the relationship between the phase diagram and the magnetic fluctuations.PACS numbers: PACS: 74.25. Ha, 74.62.Fj, 74.70.Tx, 75.30.Kz, 76.60.Gv It has been reported that a superconducting (SC) order in cerium (Ce)-based heavy-fermion (HF) compounds takes place nearby the border at which an antiferromagnetic (AF) order is suppressed by applying pressure (P ) to the HF-AF compounds CeCu 2 Ge 2 ,[1] CePd 2 Si 2 [2] and CeIn 3 [3]. The superconductivity in these compounds, however, occurs only in extreme conditions where the pressure exceeds ∼ 2 GPa and temperature (T ) is cooled down below ∼ 1 K. Indeed the experiments were restricted mainly to transport measurements. The discovery of P -induced HF superconductors in Ce-based HF-AF compounds has stimulated further experimental works under P [4,5,6,7]. In order to gain profound insight into a relationship between magnetism and superconductivity in HF systems, systematic NMR/NQR experiments under P are important, since they can probe the evolution of the magnetic properties toward the onset of SC phase.Recently, Hegger et al. found that a new HF material CeRhIn 5 consisting of alternating layers of CeIn 3 and RhIn 2 reveals an AF-to-SC transition at a relatively lower critical pressure P c = 1.63 GPa than in all previous examples [1,2,3]. The SC transition temperature T c = 2.2 K is the highest one to date among P -induced superconductors [4]. This finding has opened a way to investigate the P -induced evolution of both magnetic and SC properties over a wide P range. In the previous paper [7], the 115 In NQR study of CeRhIn 5 has clarified the P -induced anomalous magnetism and unconventional superconductivity. In the AF region, the Néel temperature T N exhibits a moderate variation, while the internal field H int at 115 In(1) site in the CeIn 3 plane due to the magnetic ordering is linearly reduced in P = 0 -1.23 GPa, extrapolated to zero at P * = 1.6 ± 0.1 GPa. This P * is comparable to P c = 1.63 GPa at which the SC signature appears [4], which was indicative of a second-order like AF-to-SC transition rather than the first-order one suggested previously [4]. At P = 2.1 GPa, it was found that the nuclear spin-lattice relaxation rate 1/T 1 reveals a T 3 dependence below the SC transition temperature T c , which shows the existence of line-nodes in the gap function [7]. It is, however, not yet clear how the electronic states change with P when the AF phase evolves into the SC phase.On the other hand, CeIn 3 c...

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