Correlation between Superconducting Transition Temperature $T_c$ and Increase of Nuclear Spin-Lattice Relaxation Rate Devided by Temperature $1/T_{1}T$ at $T_c$ in the Hydrate Cobaltate Na${}_x$CoO${}_2\cdot y$H${}_2$O

Abstract

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 were also performed on different-hydrate-content samples with different $T_c$ values, which were prepared from the same Na-content ($x$ = 0.348) sample. From measurements of $1/T_1$ using the different-hydrate-content samples, it was found that a low-$T_c$ sample with $T_c=3.9$ K has a larger residual density of states (DOS) in the SC state and a smaller increase of $1/T_{1}T$ just above $T_c$ than a high-$T_c$ sample with $T_c$ = 4.7 K. The former behavior is consistent with that observed in unconventional superconductors, and the latter suggests the relationship between $T_c$ and the increase in DOS just above $T_c$. This increase, which is seemingly associated with the two-dimensionality of the CoO${}_2$ plane, is considered to be one of the most important factors for the occurrence of superconductivity.

5 pages, 5 figures, To be published in J. Phys. Soc. Jpn

References in corpus (7)

• Superconductivity Phase Diagram of Na(x)CoO(2).1.3H(2)O
• An Electronic Model for $Co{O}_2$ layer based systems: Chiral RVB metal and Superconductivity
• Unconventional Superconductivity and Electron Correlations in Cobalt Oxyhydrate Na${}_{0.35}$CoO${}_2$$\cdot y$H${}_2$O
• Superconducting states in frustrating t-J model: A model connecting high-$T_c$ cuprates, organic conductors and Na${}_x$CoO${}_2$
• Unconventional Superconductivity and Nearly Ferromagnetic Spin Fluctuations in Na${}_x$CoO${}_2$$\cdot y$H${}_2$O
• Possibility of f-wave spin-triplet superconductivity in the CoO superconductor: a case study on a 2D triangular lattice in the repulsive Hubbard model
• 59Co-NQR study on superconducting NaxCoO2.yH2O

Cited by in corpus (11)

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• Weak Magnetic Order in the Bilayered-hydrate Na${}_x$CoO${}_2\cdot y$H${}_2$O Structure Probed by Co Nuclear Quadrupole Resonance - Proposed Phase Diagram in Superconducting Na${}_x$CoO${}_2\cdot$ $y$H${}_2$O
• 59Co Nuclear Quadrupole Resonance Studies of Superconducting and Non-superconducting Bilayer Water Intercalated Sodium Cobalt Oxides NaxCoO2.yH2O
• Ferromagnetic and triplet-pairing instabilities controlled by the trigonal distortion of the CoO_6 octahedra in Na_xCoO_2*yH_2O
• Unconventional Superconductivity Induced by Quantum Critical Fluctuations in Hydrate Cobaltate Na${}_x$(H${}_3$O)${}_z$CoO${}_x\cdot$ $y$H${}_2$O -- Relationship between Magnetic Fluctuations and the Superconductivity Revealed by a Co Nuclear Quadrupole Resonance --
• Deformation of Electronic Structures Due to CoO6 Distortion and Phase Diagrams of NaxCoO2.yH2O
• ${}^{17}$O NMR Measurements on Superconducting Na${}_{0.35}$CoO${}_2\cdot y$H${}_2$O
• Anisotropic Behavior of Knight Shift in Superconducting State of Na_xCoO_2yH_2O
• CoO2-Layer-Thickness Dependence of Magnetic Properties and Possible Two Different Superconducting States in NaxCoO2.yH2O
• Specific Heat and Superfluid Density for Possible Two Different Superconducting States in NaxCoO2.yH2O
• Identifying the pairing symmetry in sodium cobalt oxide by Andreev edge states