Article

# Unconventional superconductivity in Na$_{0.35}$CoO$_{2}\cdot$1.3D$_{2}$O and proximity to a magnetically ordered phase

04/2004;

Source: arXiv

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Graeme Luke, Apr 05, 2013 Available from: Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

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**ABSTRACT:**Motivated by the recent discovery of superconductivity in NaxCoO2.yH(2)O, we use series expansion methods and cluster mean-field theory to study spontaneous charge order, Neel order, ferromagnetic order, dimer order and phase-separation in the triangular-lattice t-J-V model at 2/3 electron density. We find that, for t<0, the charge ordered state, with electrons preferentially occupying a honeycomb lattice, is very robust. Quite surprisingly, hopping to the third sublattice can even enhance Neel order. At large negative t and small V, the Nagaoka ferromagnetic state is obtained. For large positive t, charge and Neel order vanish below a critical V, giving rise to an itinerant antiferromagnetically correlated state.Physical review. B, Condensed matter 07/2004; 70(2). DOI:10.1103/PhysRevB.70.020504 · 3.66 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**We propose that the spin-triplet pairing mechanism due to disconnected Fermi surfaces proposed in our previous study [Phys. Rev. BPRBMDO0163-1829 63, 174507 (2001)10.1103/PhysRevB.63.174507] may be at work in a recently discovered superconductor NaxCoO2·yH2O. We introduce a single band effective model that takes into account the pocketlike Fermi surfaces along with the van Hove singularity near the K point found in the band calculation results. Applying the fluctuation exchange method and solving the linearized Éliashberg equation, the most dominant pairing is found to have spin-triplet f-wave symmetry, where the nodes of the gap function do not intersect the pocket Fermi surfaces. The presence of finite Tc is suggested in sharp contrast to cases when the gap nodes intersect the Fermi surface.Physical Review Letters 08/2004; 93(7). DOI:10.1103/PhysRevLett.93.077001 · 7.51 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**The low-energy Fermi-surface states in layered cobaltate were analyzed from the Mott insulating unit. Investigations show that the fermi-surface topology at low doping were strongly influenced by the spin-orbit coupling of the correlated electrons at t2g level. It was found that the low-energy electronic states of the CoO2 layer were derived from the Kramers pseudospin doublets of the Co4+ ion. The results show that the projection of the J interaction on the pseudospin states leads to the novel pseudospin-triplet pairing.Physical Review Letters 11/2004; 93(17):176401. DOI:10.1103/PhysRevLett.93.176401 · 7.51 Impact Factor