Ferromagnetic and triplet-pairing instabilities controlled by the trigonal distortion of the CoO_6 octahedra in Na_xCoO_2*yH_2O

Abstract

In the recently discovered Co-oxide superconductor Na_xCoO_2*yH_2O, the edge-shared CoO6 octahedra are trigonally contracted along the c-axis in the CoO2-plane. We study how this CoO6 distortion affects the magnetic properties and superconductivity in this compound by analyzing the multiorbital Hubbard model using the fluctuation-exchange approximation. It is shown that through generating the trigonal crystal field, the distortion pushes the Co e'g bands up and consequently gives rise to the hole-pocket Fermi surfaces, which have been predicted in the band calculations. As the distortion increases, the hole pockets are enlarged and the ferromagnetic fluctuation as well as the pairing instability increases, which is in good agreement with recent NQR results.

5 pages, 4 figures. Errata: Ref.[10] in published version should be "Y. Kobayashi, M. Yokoi and M. Sato: J. Phys. Soc. Jpn. 72 (2003) 2161, ibid. 72 (2003) 2453"

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• 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 --
• Orbital-Controlled Superconductivity in f-Electron Systems
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• Deformation of Electronic Structures Due to CoO6 Distortion and Phase Diagrams of NaxCoO2.yH2O
• Magnetic properties of superconducting cobalt oxides NaxCoO2.yH2O
• CoO2-Layer-Thickness Dependence of Magnetic Properties and Possible Two Different Superconducting States in NaxCoO2.yH2O
• Role of spin-orbit coupling on the spin triplet pairing in Na_{x}CoO_{2}yH_{2}O I: d-vector under zero magnetic field
• Fermi-Surface Topology and Pairing Symmetry in BiS${}_2$-Based Layered Superconductors
• Fulde-Ferrell-Larkin-Ovchinnikov State in the absence of a Magnetic Field
• Specific Heat and Superfluid Density for Possible Two Different Superconducting States in NaxCoO2.yH2O
• Spin, charge, and orbital correlations in the one-dimensional t2g-orbital Hubbard model
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• Magnetic anomalies of hydrous cobaltate compound Na_x(H_3O)_zCoO_2 \cdot yH_2O detected by NMR and NQR measurements
• In-plane Anisotropy of the Magnetic Fluctuations in NaxCoO2-yH2O
• 59Co-NMR Knight Shift of Superconducting Three-Layer NaxCoO2.yH2O