Electronic model for CoO<SUB>2</SUB> layer based systems: chiral resonating valence bond metal and superconductivity

Takada et al. have reported superconductivity in layered NaxCoO2yH2O (Tc&#8776;5 K)and more recently Wen et al. in AxCoO2+&#948; (A = Na,K)(Tc&#8776;31 K). We model a reference neutral CoO2 layer as an orbitally nondegenerate spin-&#189; antiferromagnetic Mott insulator on a triangular lattice and NaxCoO2.yH2O and AxCoO2+&#948; as electron doped Mott insulators described by a t-J model. It is suggested that at optimal doping chiral spin fluctuations enhanced by the dopant dynamics lead to a gapful d-wave superconducting state. A chiral resonating valence bond (RVB) metal, a parity and time (PT) reversal violating state with condensed RVB gauge fields, with a possible weak ferromagnetism, and low temperature p-wave superconductivity are also suggested at higher dopings