59Co-NMR Knight Shift of the Superconducting NaxCoO2.yH2O

We report an NMR investigation of the superconductivity in BaFe(2)As(2) induced by Co doping (Tc=22K). We demonstrate that Co atoms form an alloy with Fe atoms and donate carriers without creating localized moments. Our finding strongly suggests that the underlying physics of iron-pnictide superconductors is quite different from the widely accepted physical picture of high Tc cuprates as doped Mott insulators. We also show a crossover of electronic properties into a low tempe...

Co NQR studies were performed in recently discovered superconductor Na$_x$CoO$_2$$\cdot y$H$_2$O to investigate physical properties in the superconducting (SC) and normal states. Two samples from the same Na$_x$CoO$_2$ were examined, SC bilayer-hydrate sample with $T_c \sim 4.7$ K and non-SC monolayer-hydrate sample. From the measurement of nuclear-spin lattice relaxation rate $1/T_1$ in the SC sample, it was found that the coherence peak is absent just below $T_c$ and that $...

Na0.5CoO2 exhibits a metal-insulator transition at 53 K upon cooling. The nature of another transition at 88 K has not been fully clarified yet. We report the results of measurements of the electrical conductivity, the magnetic susceptibility and 23Na NMR on a powder sample of Na0.5CoO2, including the mapping of NMR spectra, as well as probing the spin-lattice relaxation rate and the spin-spin relaxation rate, in the temperature range between 30 K and 305 K. The NMR data refl...

We report results of $^{59}$Co nuclear magnetic resonance measurements on a single crystal of superconducting PuCoGa5 in its normal state. The nuclear spin-lattice relaxation rates and the Knight shifts as a function of temperature reveal an anisotropy of spin fluctuations with finite wave vector q. By comparison with the isostructural members, we conclude that antiferromagnetic XY-type anisotropy of spin fluctuations plays an important role in mediating superconductivity in ...

We report 23Na NMR studies of the polycrystalline samples of bilayer hydrated cobalt oxides Na0.35CoO2-1.3H2O with the superconducting transition temperatures Tc < 1.8 and ~ 4.5 K. The magnitude of the 23Na nuclear spin-lattice relaxation rate 23(1/T1) significantly decreased from non-hydrated Na0.7CoO2 to the bilayer hydrates. We found that the temperature dependence of 23(1/T1) of the non-superconducting bilayer hydrate is similar to that of the non-hydrated Na0.7CoO2, the ...

We synthesized the five batches of the samples of the novel P3 type superconductor, Na$_{x}$(H$_{3}$O)$_{y'}$CoO$_{2}\cdot y''$H$_{2}$O, by the soft chemical process starting from $\alpha$-NaCoO$_{2}$. The chemical and structural properties varied rather widely from batch to batch, with a result that $T_{c}$ varied from 4.6 K to 3.2 K. The magnetic susceptibility above $T_{c}$ shows upturn at low temperature as in the case of the P2 phase. The $T_{c}$ seems to be well correla...

We have performed Co-nuclear quadrupole resonance (NQR) studies on Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O compounds with different Na ($x$) and hydrate ($y$) contents. Two samples with different Na contents but nearly the same $T_c$ values ($x$ = 0.348, $T_c$ = 4.7 K ; $x$ = 0.339, $T_c$ = 4.6 K) were investigated. The spin-lattice relaxation rate $1/T_1$ in the superconducting (SC) and normal states is almost the same for the two samples except just above $T_c$. NQR measurements w...

We report the in-plane resistivity and magnetic susceptibility of the layered cobalt oxide Na$_{0.35}$CoO$_{2}{\cdot}1.3$H$_{2}$O single crystal. The temperature dependence of the resistivity shows metallic behavior from room temperature to the superconducting transition temperature $T_{c}$ of 4.5 K. Sharp resistive transition, zero resistivity and almost perfect superconducting volume fraction below $T_{c}$ indicate the good quality and the bulk superconductivity of the sing...

Nuclear-magnetic-resonance (NMR) studies were performed in Na$_{0.7}$CoO$_2$ to investigate its magnetic properties from the microscopic point of view. Na$_{0.7}$CoO$_2$ is a starting compound of the recently discovered superconductor Na$_{0.35}$CoO$_2$$\cdot 1.3$H$_2$O, in which Co atoms form a triangular structure. Although $^{23}$Na-NMR results show no magnetic anomaly down to 1.5 K, Knight shift ($^{23}K$) and $^{23}(1/T_1T)$ of $^{23}$Na continue to increase, suggestive ...

The superconducting property of recently discovered sodium cobalt oxyhydrate, Na$_{0.35}$CoO$_2$1.3H$_2$O ($T_c=4.5$ K), has been studied by means of muon spin rotation/relaxation ($\mu$SR) down to 2 K. It was found that the zero-field muon spin relaxation rate is independent of the temperature, indicating that no static magnetism appears in this compound, at least above 2 K. The result also provides evidence against the breakdown of time-reversal symmetry for the superconduc...