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.
@article{arxiv.cond-mat/0407587,
title = {Competition between singlet and triplet pairings in Na_xCoO_2 yH_2O},
author = {Kazuhiko Kuroki and Yukio Tanaka and Ryotaro Arita},
journal= {arXiv preprint arXiv:cond-mat/0407587},
year = {2009}
}