Koh-ichi Ueda

29Si knight shift in the heavy-Fermion superconductor CeCu2Si2

We present a study of 29 Si and 63 Cu Knight shifts in the superconducting CeCu 2 Si 2 . The shifts K ∥ , parallel and K ⊥ perpendicular to the tetragonal c -axis were obtained from the anisotropic 29 Si NMR sectrum. K ⊥ shows a rapid decrease below T c ( H )=0.66 K, while the change of K ∥ is not well resolved. K ∥ at 0.2 K decreases to 40%of the value at T c ( H ). Furthermore, the distinct decrease of K ∥ and K ⊥ has also been observed for 63 Cu below T c . The strong reduction of the shift, which is independent of the direction of the crystallographic axis, supports the model of even-parity pairing without significant spin-orbit scattering by impurities, although the energy gap has an anisotropic nature, as is demonstrated by the nuclear relaxation study.

NQR and NMR studies of Cu in the superconducting La2CuO4+δ

Abstract In the superconducting La2CuO4+δ obtained by annealing in high pressure mixture gas of oxygen and argon, nuclear quadrupole resonance (NQR) signals of 63Cu and 65Cu have been observed around 33.1 and 36.0 MHz together with the antiferromagnetic Cu NMR signal around 70–100 MHz. The ratio of the resonance frequency of 63Cu and 65Cu is the same as that of the quadrupole moment of each Cu nucleus, indicating no internal magnetic field (paramagnetic) at Cu site. The nuclear spin-lattice relaxation time, T1, of Cu NQR indicates that the paramagnetic phase is in the superconducting state at low temperatures. The NQR intensity is roughly proportional to the partial pressure of the oxygen gas. The NQR result suggests that the volume fraction of paramagnetic phase in La2CuO4+δ increases with increasing oxygen content.

NMR investigation of superconductivity and Kondo-coherency in CeCu2Si2

In the normal dense Kondo state of CeCu 2 Si 2 , the nuclear magnetic relaxation rate 1/ T 1 of 63 Cu divided by T , 1/ T 1 T is almost constant below 2.5 K with a slight increase near the superconducting transition temperature. Together with the results of other normal Kondo lattice compounds, it is concluded that the temperature dependence of 1/ T 1 T at low temperatures does not scale to that of the specific heat divided by T , C ( T )/ T in Kondo lattice compounds in contrast with the case of dilute Kondo impurities. In the superconducting state, 1/ T 1 T varies as T 2 , suggesting the gap zeros along lines, while the reported data of C s ( T )/ T show no simple power law dependence. It is claimed that this difference below T c may be correlated with the difference between 1/ T 1 T and C ( T )/ T in the normal dense Kondo state.

NMR study of electronic state in CePt3SiCePt3Si

In this article, we report the temperature dependence of spin-lattice relaxation rates at two Pt sites and one Si site in CePt 3 Si with a non-centrosymmetric structure center. 1/T 1 for both Pt sites between 2 and 300 K and 1/T 1 of Si above 3 K might be explained by the contributions from the low-lying crystal-electric-field level and the quasi-particle due to the hybridization between the ground state and conduction electrons. Just below T c no remarkable enhancement in 1/T 1 was observed. The estimated value of superconducting gap is about 2Δ = 3k B T c .

Cu NQR and Pb NMR in the superconducting Pb2Sr2Y1−xCaxCu3O8+δ

A pair of sharp Cu NQR signals and a broad Cu NQR signal were observed in high-T c Pb cuprate. In the superconducting state, 1/T 1 of Cu2 site decreases rapidly without enhancement just below T c , which is similar to those for the CuO 2 planes in Y-, La- and Bi-systems. The difference of the measured 1/T 1 between both Cu sites in the normal state may be due to the difference of the density of states between them, supporting the recent band calculation result.

Cu NQR study in Bi2Sr2CuO6

Abstract Cu NQR study has been carried out in Bi 2 Sr 2 CuO 6 to obtain information on the normal state of Bi-based high-T c superconductors over a wide temperature range. NQR signal broadened by the structural modulation is observed between 25 and 35MHz. The nuclear spin lattice relaxation rate, 1/T 1 , was measured. 1/T 1 is proportional to temperature below 10K. With increasing temperature, 1/T 1 has a tendency to be saturated above 15K.

NMR study of electronic state in

In this article, we report the temperature dependence of spin-lattice relaxation rates at two Pt sites and one Si site in CePt 3 Si with a non-centrosymmetric structure center. 1/T 1 for both Pt sites between 2 and 300 K and 1/T 1 of Si above 3 K might be explained by the contributions from the low-lying crystal-electric-field level and the quasi-particle due to the hybridization between the ground state and conduction electrons. Just below T c no remarkable enhancement in 1/T 1 was observed. The estimated value of superconducting gap is about 2Δ = 3k B T c .

Depression of the superconducting transition temperature in neutron irradiated La2CuO4+δ

Abstract The influence of neutron irradiation to the superconductivity of the oxygen loaded La 2 CuO 4+ δ , which were prepared from one single crystal of La 2 CuO 4 , was investigated. The neutron irradiation were performed at 10 K. The superconducting transition temperature ( T c ) dropped monotonously with increasing the neutron fluence. The depression rate of T c was −1.3 K/10 17 n/cm 2 . A rise of T c could not be observed by the neutron irradiation.

Existence of the mixed phases in Er-Pb system

Abstract Pb NMR was carried to get a detailed electronic state in the recently reported ErPb2. Pb NMR results have revealed that most parts of ErPb2 are not the coexistent compound of the superconductivity and the antiferromagnetic ordering, but a mixture of superconducting Pb (or Pb-rich) region and an antiferromagnetic Er compound (or alloy). Some models on the structure in ErPb system are proposed.

Nuclear magnetic resonance study of some Ce-based superconductors with noncentrosymmetric crystal structure

NMR experiments on two kinds of Ce-based superconductors with noncentrosymmetry in the crystal structures were performed. They are CePt3Si and CeIr0.65Co0.35Si3 with 0.75 and 0.55 K of Tc’s, respectively. By annealing of the crushed sample, CePt3Si recovers two distinct phases, which are coexistent in the crystal, and one of two phases gets the improved characters of single crystal. The angular dependence of an aligned axis and an applied magnetic field exhibits that the internal field must be parallel to the c-axis at Si site below TN, which appears to be inconsistent with the results obtained by the neutron diffraction. On the other hand, a CeIr0.65Co0.35Si3 sample with noncentrosymmetry also shows a clear Meissner diamagnetization at 0.55 K under an ambient pressure and yields a clear Co NMR spectrum with an electric quadrupole splitting.