We report the results of a Te-125 NMR study of single crystalline Pb1-xTlxTe (x = 0, 0.35, 1.0%) as a window on the novel electronic states associated with the thallium impurities in PbTe. The Knight shift is enhanced as x increases, corresponding to an increase in the average density of states (DOS) coupled to a strong spatial variation in the local DOS surrounding each Tl dopant. Remarkably, for the superconducting composition (x = 1.0%), the Te-125 nuclear spin relaxation rate (1/T1T) for Te ions that are close to the Tl dopants is unexpectedly enhanced in the normal state below a characteristic temperature of similar to 10 K, below which the resistivity experiences an upturn. Such a simultaneous upturn in both the resistivity and (1/T1T) was not suppressed in the high magnetic field. We suggest that these observations are consistently accounted for by dynamical charge fluctuations in the absence of paramagnetism, which is anticipated by the charge Kondo scenario associated with the Tl dopants. In contrast, such anomalies were not detected in the non-superconducting samples (x = 0 and 0.35%), suggesting a connection between dynamical valence fluctuations and the occurrence of superconductivity in Pb1-xTlxTe.

We report the results of a Te NMR study of single crystalline Pb1−xTlxTe (x=0, 0.35, 1.0%) as a window on the novel electronic states associated with the thallium impurities in PbTe. The Knight shift is enhanced as x increases, corresponding to an increase in the average density of states (DOS) coupled to a strong spatial variation in the local DOS surrounding each Tl dopant. Remarkably, for the superconducting composition (x=1.0%), the Te nuclear spin relaxation rate (1/T1T ) for Te ions that are close to the Tl dopants is unexpectedly enhanced in the normal state below a characteristic temperature of ∼10 K, below which the resistivity experiences an upturn. Such a simultaneous upturn in both the resistivity and (1/T1T ) was not suppressed in the high magnetic field. We suggest that these observations are consistently accounted for by dynamical charge fluctuations in the absence of paramagnetism, which is anticipated by the charge Kondo scenario associated with the Tl dopants. In contrast, such anomalies were not detected in the non-superconducting samples (x=0 and 0.35%), suggesting a connection between dynamical valence fluctuations and the occurrence of superconductivity in Pb1−xTlxTe.

We report on superconducting nature under pressure in CeIr(In1–xCdx)5 by In-Nuclear-Quadrupole-Resonance (NQR) studies. In CeIr(In0.925Cd0.075)5, the inhomogeneous antiferromagnetic order at TN ∼ 2.3 K is induced by Cd-dopants and superconductivity disappears at ambient pressure. However, the measurements of a nuclear-spin-lattice-relaxation rate 1/T1 have revealed that the superconductivity suddenly occurs above 2.1 GPa. It is observed that the superconducting gap is enhanced in the Cd-doped sample, indicating that the Cd-doping induces the strong coupling superconductivity leading to the enhancement of Tc in the CeIrIn5 system. Furthermore, we found that the residual density of states at the Fermi level increases with increasing pressure, suggesting that the superconducting nature of CeIrIn5 is quite different from those of CeCoIn5 and CeRhIn5.

We report on P-31-NMR studies of LaFe(As1-xPx)(O1-yFy) over wide compositions for 0 <= x <= 1 and 0 <= y <= 0.14, which provide clear evidence that antiferromagnetic spin fluctuations (AFMSFs) are one of the indispensable elements for enhancing T-c. Systematic P-31-NMR measurements revealed two types of AFMSFs in the temperature evolution, that is, one is the AFMSFs that develop rapidly down to T-c with low-energy characteristics, and the other, with relatively higher energy than the former, develops gradually upon cooling from high temperature. The low-energy AFMSFs in low y (electron doping) over a wide x (pnictogen height suppression) range are associated with the two orbitals of d(xz/yz), whereas the higher-energy ones for a wide y region around low x originate from the three orbitals of d(xy) and d(xz/yz). We remark that the nonmonotonic variation of T-c as a function of x and y in LaFe(As1-xPx)(O1-yFy) is attributed to these multiple AFMSFs originating from degenerated multiple 3d orbitals inherent to Fe-pnictide superconductors.

We report Cu-63- and Tl-205-NMR studies on six-layered (n = 6) high-T-c superconducting (SC) cuprate TlBa2Ca5-Cu6O14+delta (Tl1256) with T-c similar to 100 K, which reveal that antiferromagnetic (AFM) order takes place below T-N similar to 170 K. In this compound, four underdoped inner CuO2 planes [n(IP) = 4] sandwiched by two outer planes (OPs) are responsible for the onset of AFM order, whereas the nearly optimally-doped OPs responsible for the onset of bulk SC. It is pointed out that an increase in the out-of-plane magnetic interaction within an intra-unit-cell causes T-N similar to 45K for Tl1245 with n(IP) = 3 to increase to similar to 170K for Tl1256 with n(IP) = 4. It is remarkable that the marked increase in TN and the AFM moments for the IPs does not bring about any reduction in T-c, since T-c similar to 100K is maintained for both compounds with nearly optimally doped OP. We highlight the fact that the SC order for n >= 5 is mostly dominated by the long-range in-plane SC correlation even in the multilayered structure, which is insensitive to the magnitude of T-N and the AFM moments at the IPs or the AFM interaction among the IPs. These results demonstrate a novel interplay between the SC and AFM orders when the charge imbalance between the IPs and OP is significantly large.

We report on the Ge-73-nuclear magnetic resonance (NMR)/nuclear quadrupole resonance (NQR) results for the ferromagnetic (FM) superconductor URhGe. The magnitude and direction of the internal field, H-int, and the parameters of the electric field gradient at the Ge site were determined experimentally. By using powdered polycrystalline samples oriented by different methods, the field dependences of NMR shift and nuclear spin relaxation rates for H-0 parallel to c (easy axis) and H-0 parallel to b were obtained. From the NMR shifts for H-0 parallel to b, we confirmed a gradual suppression of the Curie temperature and observed a phase separation near the spin reorientation. The observation of the phase separation gives microscopic evidence that the spin reorientation under H-0 parallel to b is of first order at low temperatures. The nuclear spin lattice relaxation rate 1/T-1 indicates that the magnetic fluctuations are suppressed for H-0 parallel to c, whereas the fluctuations remain strongly for H-0 parallel to b. The enhancements of both 1/T1T and the nuclear spin-spin relaxation rate 1/T-2 for H-0 parallel to b toward the spin reorientation field suggest that the field-induced superconductivity in URhGe emerges under the magnetic fluctuations along the b- and c-axes.

We report 73Ge-NMR and NQR results for ferromagnetic (FM) superconductor URhGe. The magnitude and direction of the internal field, H_int, and parameters of the electric field gradient at the Ge site were determined experimentally. Using powdered polycrystalline samples oriented by different methods, the field dependences of NMR shift and nuclear spin relaxation rates for H_0 // c (easy axis) and H_0 // b were obtained. From the NMR shifts for H_0 // b, we confirmed a gradual suppression of the Curie temperature and observed a phase separation near the spin reorientation. The observation of the phase separation gives microscopic evidence that the spin reorientation under H_0 // b is of first order at low temperatures. The nuclear spin-lattice relaxation rate 1/T_1 indicates that the magnetic fluctuations are suppressed for H_0 // c, whereas the fluctuations remain strongly for H_0 // b. The enhancements of both 1/T_1T and the nuclear spin-spin relaxation rate 1/T_2 for H_0 // b toward the spin reorientation field suggest that the field-induced superconductivity in URhGe emerges under the magnetic fluctuations along the b axis and the c axis.

that a hole density p(IP) (p(OP)) at the inner (IP) (outer (OP)) plane is significantly smaller (larger) than an optimal hole density p = 0:16, at which Tc exhibits a maximum. It differs significantly from the result on optimally doped Hg1223 with Tc=133 K, in which p(IP) and p(OP) are both rather close to p=0.16. Based on the accumulated results on multilayered cuprates(n= 3 5), we suggest that this large imbalance between p(IP) and p(OP) is one of the important factors for the suppression of the bulk Tc. We suggest experimentally that Tc might be enhanced up to around 160 K in cuprates if every layer in the multilayered structure(n= 3 5) could be optimally doped with p=0.16.

We revealed novel phase deagram of Fe-pnictide high-Tc superconductor LaFe(As_{1-x}P_{x})O in wide doping level (0.3<x<1) by P-NMR. Systematic 31P-NMR studies revealed the emergence of the antiferromagnetic ordered phase (AFM-2) in 0.4 < x < 0.7 that intervenes between two superconductivity (SC-1/SC-2) phases. The 31P-NMR Knight shift points to the appearance of the sharp density of states at the Fermi level that is derived from d_{3Z^2?r^2} orbit, which is less relevant with the onset of the SC-2. On the other hand, we remark that the AFM spin fluctuations arising from the interband nesting on the d_{XZ}/d_{YZ} orbits must be a key ingredient for the occurrence of SC around AFM-2.

We performed an 121 Sb-NMR measurement on CeOs 4 Sb 12 . The temperature ( T ) dependence of its Knight shift was studied in detail by using an aligned powdered sample and two sets of NQR parameters. A c – f hybridization gap model with the same gap magnitude as that obtained by considering the nuclear spin–lattice relaxation rate 1/ T 1 cannot explain the Knight shift above ∼ 70 K. This may be because of the existence of q -dependent spin fluctuations. The increase in the Knight shift with decreasing temperatures below ∼ 70 K revealed a ferromagnetic correlation. This result and previous 1/ T 1 measurements indicate the presence of both ferromagnetic and antiferromagnetic fluctuations that may be related to an anomalous ordered phase in CeOs 4 Sb 12

We report an 75As-NMR study on iron (Fe)-based superconductors with thick perovskitetype blocking layers Sr4(Mg0.5-xTi0.5+x)2O6Fe2As2 with x=0 and 0.2. We have found that antiferromagnetic (AFM) order takes place when x=0, and superconductivity (SC) emerges below Tc=36 K when x=0.2. These results reveal that the Fe-pnictides with thick perovskitetype blocks also undergo an evolution from the AFM order to the SC by doping electron carriers into FeAs planes through the chemical substitution of Ti+4 ions for Mg+2 ions, analogous to the F-substitution in LaFeAsO compound. The reason why the Tc=36 K when x=0.2 being higher than the optimally electron-doped LaFeAsO with Tc=27 K relates to the fact that the local tetrahedron structure of FeAs4 is optimized for the onset of SC.

We report 75 As-nuclear quadrupole resonance (NQR) and 57 Fe-nuclear magnetic resonance (NMR) studies on heavily electron-doped LaFeAsO-based compounds with T c =5 and 8 K. The high quality of the samples was ensured by both narrow 57 Fe-NMR and 75 As-NQR spectra despite in the heavily overdoped state. Nuclear spin relaxation rate (1/ T 1 ) measurements by 75 As-NQR at zero field has revealed that a coherence peak just below T c partially recovers in heavily electron-overdoped regimes where the nesting condition of hole and electron Fermi surfaces (FSs) becomes significantly worse. This result suggests that the interband scattering between the hole and electron FSs is suppressed by the heavily electron-overdoping because the hole FSs become smaller.

We report on an (75)As-NMR study on the Fe-pnictide high-T(c) superconductor Y(0.95)La(0.05)FeAsO(1-y) (Y(0.95)La(0.05)1111) with T(c)=50 K that includes no magnetic rare-earth elements. The measurement of the nuclear-spin lattice-relaxation rate (75)(1/T(1)) has revealed that the nodeless bulk superconductivity takes place at T(c)=50 K while antiferromagnetic spin fluctuations develop moderately in the normal state. These features are consistently described by the multiple fully gapped s(±)-wave model based on the Fermi-surface nesting. Incorporating the theory based on band calculations, we propose that the reason that T(c)=50 K in Y(0.95)La(0.05)1111 is larger than T(c)=28 K in La1111 is that the Fermi-surface multiplicity is maximized, and hence the Fermi-surface nesting condition is better than that in La1111.

We performed an Sb-121-NMR measurement on CeOs4Sb12. The temperature (T) dependence of its Knight shift was studied in detail by using an aligned powdered sample and two sets of NQR parameters. A c-f hybridization gap model with the same gap magnitude as that obtained by considering the nuclear spin-lattice relaxation rate 1/T-1 cannot explain the Knight shift above similar to 70 K. This may be because of the existence of q-dependent spin fluctuations. The increase in the Knight shift with decreasing temperatures below similar to 70 K revealed a ferromagnetic correlation. This result and previous 1/T-1 measurements indicate the presence of both ferromagnetic and antiferromagnetic fluctuations that may be related to an anomalous ordered phase in CeOs4Sb12

We report a pressure-induced evolution of magnetism and superconductivity in a helical magnet CeRhIn 5 with an incommensurate wave vector Q i =(1/2,1/2,0.297) through the 115 In nuclear quadrupole resonance (NQR) measurements under P . From systematic measurements of the 115 In-NQR spectrum, it is suggested that the commensurate antiferromagnetic order with Q c =(1/2,1/2,1/2) is realized near an antiferromagentic quantum critical point. The homogeneous coexistence of superconductivity and the commensurate antiferromagnetism is observed from the measurements of a nuclear spin–lattice relaxation rates (1/ T 1 ) at 1.82 GPa. The analysis for 1/ T 1 data below T c indicates that the strong coupling superconductivity is realized above an antiferromagnetic quantum critical point.

We report systematic Cu- and F-NMR measurements of five-layered high-Tc cuprates Ba2Ca4Cu5O10(F,O)2. It is revealed that antiferromagnetism (AFM) uniformly coexists with superconductivity (SC) in underdoped regions, and that the critical hole density pc for AFM is ~ 0.11 in the five-layered compound. We present the layer-number dependence of AFM and SC phase diagrams in hole-doped cuprates, where pc for n-layered compounds, pc(n), increases from pc(1) ~ 0.02 in LSCO or pc(2) ~ 0.05 in YBCO to pc(5) ~ 0.11. The variation of pc(n) is attributed to interlayer magnetic coupling, which becomes stronger with increasing n. In addition, we focus on the ground-state phase diagram of CuO2 planes, where AFM metallic states in slightly doped Mott insulators change into the uniformly mixed phase of AFM and SC and into simple d-wave SC states. The maximum Tc exists just outside the quantum critical hole density, at which AFM moments on a CuO2 plane collapse at the ground state, indicating an intimate relationship between AFM and SC. These characteristics of the ground state are accounted for by the Mott physics based on the t-J model; the attractive interaction of high-Tc SC, which raises Tc as high as 160 K, is an in-plane superexchange interaction Jin (~ 0.12 eV), and the large Jin binds electrons of opposite spins between neighboring sites. It is the Coulomb repulsive interaction U ~ (> 6 eV) between Cu-3d electrons that plays a central role in the physics behind high-Tc phenomena.