Isotope Effect on Superconducting Transition Temperature of NaxCoO2 .yH2O

The effect of 16 O→ 18 O substitution on the superconducting transition temperature T c of Na x CoO 2 · y H 2 O has been studied for several sets of samples. Each set has two kinds of samples, one with oxygen sites in CoO 2 layers filled with 16 O atoms and the other with these sites partially substituted with 18 O isotopes. These two kinds of samples were prepared in parallel in whole preparation processes. For all the sample sets, we have not found any significant difference in T c between the nonsubstituted and substituted samples, which indicates that the oxygen isotope effect is not appreciable in Na x CoO 2 · y H 2 O. Arguments on what this result indicates are presented.

[1]  K. Yada,et al.  s-wave Superconductivity due to Suhl-Kondo Mechanism in Na$_x$CoO$_2\cdot y$H$_2$O: Effect of Coulomb Interaction and Trigonal Distortion , 2008, 0801.3495.

[2]  M. Yokoi,et al.  T–3νQ Phase Diagram of Hydrated Cobalt Oxides NaxCoO2·yH2O , 2007 .

[3]  K. Ishizaka,et al.  Angle-resolved photoemission study of the cobalt oxide superconductor Na(x)CoO(2) x yH(2)O: observation of the Fermi surface. , 2006, Physical review letters.

[4]  C. Lin,et al.  Spin singlet pairing in the superconducting state of NaxCo02 1.3H2O: evidence from a 59Co Knight shift in a single crystal , 2006, cond-mat/0605212.

[5]  R. Arita,et al.  Extended s -wave pairing originating from the a 1g band in Na x CoO 2 ∙yH 2 O : Single-band U-V model with fluctuation exchange method , 2006 .

[6]  Hidekazu Watanabe,et al.  Magnetic properties of superconducting cobalt oxides NaxCoO2·yH2O , 2006, cond-mat/0602323.

[7]  Y. Itoh,et al.  59Co Nuclear Quadrupole Resonance Studies of Superconducting and Nonsuperconducting Bilayer Water Intercalated Sodium Cobalt Oxides NaxCoO2·yH2O , 2006, cond-mat/0601659.

[8]  K. Yada,et al.  Electron–Phonon Mechanism for Superconductivity in Na0.35CoO2: Valence-Band Suhl–Kondo Effect Driven by Shear Phonons , 2005, cond-mat/0512440.

[9]  M. Avdeev,et al.  Superconductivity and cobalt oxidation state in metastable Na{sub x}CoO{sub 2-{delta}}{center_dot}yH{sub 2}O (x{approx_equal}1/3; y{approx_equal}4x) , 2005 .

[10]  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 .

[11]  Hidekazu Watanabe,et al.  59Co-NMR Knight Shift of Aligned Crystals and Polycrystalline Samples of Superconducting Na0.3CoO2 1.3H2O , 2004, cond-mat/0412466.

[12]  Jinlong Yang,et al.  First-principles lattice dynamics of NaCo O 2 , 2004, cond-mat/0402497.

[13]  Y. Kobayashi,et al.  Impurity Effects on the Superconducting Transition Temperature of NazCoO2·yH2O , 2003, cond-mat/0312242.

[14]  M. Ogata,et al.  Superconductivity in NaxCoO2 yH2O due to Charge Fluctuation , 2003, cond-mat/0311266.

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

[16]  Dung-Hai Lee,et al.  Doped t-J model on a triangular lattice: Possible application to Na x CoO 2 ⋅yH 2 O and Na 1-x TiO 2 , 2003, cond-mat/0304377.

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

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

[19]  D. Singh,et al.  Quantum critical behavior and possible triplet superconductivity in electron-doped CoO 2 sheets , 2003, cond-mat/0304532.

[20]  M. Ogata.  Superconducting states in frustrating t-J model: A model connecting High-Tc cuprates, organic conductors and NaxCoO2 , 2003, cond-mat/0304405.

[21]  A. Tanaka,et al.  Possible spin triplet superconductivity in NaxCoO2.yH2O. , 2003, Physical review letters.

[22]  B. Kumar,et al.  Superconductivity in CoO 2 layers and the resonating valence bond mean-field theory of the triangular lattice t-J model , 2003, cond-mat/0304210.

[23]  G. Baskaran.  Electronic model for CoO2 layer based systems: chiral resonating valence bond metal and superconductivity. , 2003, Physical review letters.

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

[25]  W. L. Mcmillan.  TRANSITION TEMPERATURE OF STRONG-COUPLED SUPERCONDUCTORS. , 1968 .