17O NMR Measurements on Superconducting Na0.35CoO2·yH2O

An 17 O NMR measurement was performed on nonoriented polycrystalline Na 0.35 CoO 2 · y H 2 O with superconducting (SC) transition temperature T c = 4.6 K. A weak temperature dependence was observed in the Knight shift at the O site ( 17 K ). The spin part of 17 K ( 17 K spin ) is estimated from the plot of 17 K against bulk susceptibility χ. The 17 K spin decreases in the SC state, indicative of the decrease in the in-plane component of the spin susceptibility. The nuclear spin–lattice relaxation rate 1/ T 1 at the O site 17 (1/ T 1 ) shows a good scaling with 1/ T 1 at the Co site 59 (1/ T 1 ). This indicates that the spin fluctuations at the O site originate from the Co spin dynamics. The relationships between 17 (1/ T 1 T ) and 17 K spin and between 17 (1/ T 1 T ) and 59 (1/ T 1 T ) show the development of incommensurate fluctuations at q ∼ 0 other than q = 0 below 30 K. A clear indication of ferromagnetic correlations at q = 0 was not observed from the present 17 O NMR studies.

[1]  K. Masaki,et al.  Weak Magnetic Order in Bilayered-Hydrate NaxCoO2·yH2O Structure Probed by Co Nuclear Quadrupole Resonance –Proposed Phase Diagram in Superconducting NaxCoO2·yH2O– , 2005 .

[2]  T. Imai,et al.  17O NMR studies of a triangular-lattice superconductor NaxCoO2 x yH(2)O. , 2005, Physical review letters.

[3]  M. Mochizuki,et al.  Multi-orbital Analysis on the Superconductivity in NaxCoO2 yH2O , 2004, cond-mat/0407563.

[4]  M. Mochizuki,et al.  Ferromagnetic fluctuation and possible triplet superconductivity in NaxCoO2.yH2O: fluctuation-exchange study of the multiorbital Hubbard model. , 2004, Physical review letters.

[5]  T. Togashi,et al.  Laser-excited ultrahigh-resolution photoemission spectroscopy of Na x CoO 2 · y H 2 O : Evidence for pseudogap formation , 2004, cond-mat/0406632.

[6]  K. Ishida,et al.  Correlation between Superconducting Transition Temperature Tc and Increase of Nuclear Spin–Lattice Relaxation Rate Devided by Temperature 1/T1T at Tc in the Hydrate Cobaltate NaxCoO2·yH2O , 2004, cond-mat/0407192.

[7]  H. Ikeda,et al.  Possibility of f-Wave Spin-Triplet Superconductivity in the CoO2 Superconductor: A Case Study on a 2D Triangular Lattice in the Repulsive Hubbard Model , 2003, cond-mat/0308472.

[8]  J. Cmaidalka,et al.  Unconventional superconductivity and electron correlations in the cobalt oxyhydrate Na0.35CoO2.yH2O from nuclear quadrupole resonance. , 2003, Physical review letters.

[9]  J. Cho,et al.  Thermodynamic and transport measurements of superconducting Na0.3CoO2.1.3H2O single crystals prepared by electrochemical deintercalation. , 2003, Physical Review Letters.

[10]  Y. Maeno,et al.  Unconventional Superconductivity and Nearly Ferromagnetic Spin Fluctuations in NaxCoO2·yH2O , 2003, cond-mat/0308506.

[11]  M. Yokoi,et al.  59Co-NMR Knight Shift of Superconducting NaxCoO2·yH2O , 2003, cond-mat/0306264.

[12]  T. Sasaki,et al.  Unconventional upper- and lower-critical fields and normal-state magnetic susceptibility of the superconducting compound Na 0.35 CoO 2 ⋅ 1.3 H 2 O , 2003, cond-mat/0304503.

[13]  Kazunori Takada,et al.  Superconductivity in two-dimensional CoO2 layers , 2003, Nature.

[14]  K. Ishida,et al.  Cu NMR and NQR Studies of Impurities-Doped YBa2(Cu1-xMx)3O7 (M=Zn and Ni) , 1993 .