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Competition between singlet and triplet pairings in NaxCoO2 yH2O

Kazuhiko Kuroki, Yukio Tanaka, Ryotaro Arita

cond-mat.str-elarXiv:cond-mat/0407587

Abstract

We discuss the pairing symmetry of a cobaltate superconductor NaxCoO2· y H2O by adopting an effective single band model that takes into account the eg' hole pockets, as discussed in our previous paper [to appear in Phys. Rev. Lett.] Here we consider the off-site repulsions in addition to the on-site repulsion considered in our previous study. We show that the spin-triplet f-wave pairing proposed in our previous study is robust to some extent even in the presence of off-site repulsions. However, f-wave pairing gives way to singlet pairings for sufficiently large values of off-site repulsions. Among the singlet pairings, i-wave and extended s-wave pairings are good candidates which do not break time reversal symmetry below Tc in agreement with the experiments.

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