Electronic Model forCoO2Layer Based Systems: Chiral Resonating Valence Bond Metal and Superconductivity

Abstract

Takada et al. have reported superconductivity in layered ${\mathrm{N}\mathrm{a}}_x{\mathrm{C}\mathrm{o}\mathrm{O}}_{2}y{\mathrm{H}}_2\mathrm{O}$ ($T_c\approx 5\mathrm{K}$). We model a reference neutral ${\mathrm{C}\mathrm{o}\mathrm{O}}_2$ layer as an orbitally nondegenerate spin-$\frac{1}{2}$ antiferromagnetic Mott insulator on a triangular lattice and ${\mathrm{N}\mathrm{a}}_x{\mathrm{C}\mathrm{o}\mathrm{O}}_{2}y{\mathrm{H}}_2\mathrm{O}$ 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.