Unified Origin for the 3D Magnetism and Superconductivity inNaxCoO2

Abstract

We analyze the origin of the three-dimensional (3D) magnetism observed in nonhydrated Na-rich Na(x)CoO2 within an itinerant spin picture using a 3D Hubbard model. The origin is identified as the 3D nesting between the inner and outer portions of the Fermi surface, which arise due to the local minimum structure of the a(1g) band at the Gamma-A line. The calculated spin wave dispersion strikingly resembles the neutron scattering result. We argue that this 3D magnetism and the spin fluctuations responsible for superconductivity in the hydrated systems share essentially the same origin.

Competition between singlet and triplet pairings inNaxCoO2·yH2Kuroki1, Tanaka2, Arita3 2005Phys. Rev. BSelf Cite

“…In a recent study, 18 we have looked at the band calculation results of Na x CoO 2 34 from this point of view, where we find that the pocket-like Fermi surfaces (hole pockets) near the K and K ′ points (as in the bottom figure of Fig.1(b)), originating from the band having e ′ g character to some extent in the notation of ref. 34 (denoted by the thick line in Fig.2(a)), are disconnected in a similar sense as in the triangular lattice, namely the nodes of the fwave gap do not intersect the Fermi surfaces (although they do intersect the large Fermi surface around the Γ point originating from the bands having a 1g character).…”

“…18, we have adopted a model where we separate out the portion of the bands which has e ′ g character to some extent, and in particular focus only on the upper e ′ g band, which contributes to the formation of the pocket Fermi surfaces and to the large DOS at the vHS, while neglecting the lower e ′ g band, which has only small DOS near the Fermi level due to the linear dispersion at the band top. Although this portion of the band, shown by the thick curves in Fig.2(a), is disconnected between M and Γ points due to a 1g -e ′ g hybridization, it originally comes from a single band having e ′ g character, as can be understood from the inset of Fig.2(a), where a tight binding band dispersion is given for a case when large a 1g -e ′ g level offset is introduced.…”

Search for Magnetic Excitation Spectra of NaxCoO2·yD2O –Neutron Scattering–

“…Up to now, various symmetries of the order parameter have been theoretically proposed. [2][3][4][5][6][7] Experimental studies have also been carried out intensively for both hydrated and non-hydrated systems. Among these studies, NMR measurements on polycrystalline and/or single-crystal samples have been applied to investigate the symmetry of the order parameter [8][9][10][11][12][13] and specific-heat (C) measurements have also been carried out.…”

Pressure dependence of the superconducting transition and electron correlations inNaxCoO2∙1.3H2OKusano1, Kawasaki2, Matano3 et al. 2007Phys. Rev. B7070View full textAdd to dashboardCite

“…On the other hand, at pressures above 1.93 GPa, the DOS decreases with increasing P, while is less P dependent, suggesting that the reduction of T c at high pressures is primarily due to the reduction of the DOS. Although several mechanisms for the superconductivity, [14][15][16][17][18][19] including electron-lattice interaction, 14 and a charge-order-driven mechanism, 15 have been proposed, our result indicates that the Co electronic state ͑namely, the DOS͒ and magnetic fluctuations of likely antiferromagnetic origin are primarily responsible for the superconductivity.…”