CoO2-Layer-Thickness Dependence of Magnetic Properties and Possible Two Different Superconducting States in NaxCoO2.yH2O

Abstract

In order to understand the experimentally proposed phase diagrams of NaxCoO2.yH2O, we theoretically study the CoO2-layer-thickness dependence of magnetic and superconducting (SC) properties by analyzing a multiorbital Hubbard model using the random phase approximation. When the Co valence (s) is +3.4, we show that the magnetic fluctuation exhibits strong layer-thickness dependence where it is enhanced at finite (zero) momentum in the thicker (thinner) layer system. A magnetic order phase appears sandwiched by two SC phases, consistent with the experiments. These two SC phases have different pairing states where one is the singlet extended s-wave state and the other is the triplet p-wave state. On the other hand, only a triplet p-wave SC phase with dome-shaped behavior of Tc is predicted when s=+3.5, which is also consistent with the experiments. Controversial experimental results on the magnetic properties are also discussed.

5 pages, 4 figures. Submitted to Journal of the Physical Society of Japan

References in corpus (6)

• Ferromagnetic fluctuation and possible triplet superconductivity in Na_xCoO_2*yH_2O: Fluctuation-exchange study of multi-orbital Hubbard model
• Spin singlet pairing in the superconducting state of NaxCoO2\cdot1.3H2O: evidence from a ^{59}Co Knight shift in a single crystal
• 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
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• Specific Heat and Superfluid Density for Possible Two Different Superconducting States in NaxCoO2.yH2O
• Dynamical magnetic susceptibility in the lamellar cobaltate superconductor Na_xCoO_2$\cdot y$H_2O