An Electronic Model for $CoO_2$ layer based systems: Chiral RVB metal and Superconductivity

TL;DR

This paper models layered cobalt oxide systems as doped Mott insulators, proposing that chiral spin fluctuations induce d-wave superconductivity and predicting a chiral RVB metallic state with potential weak ferromagnetism and p-wave pairing.

Contribution

It introduces a theoretical model for cobalt oxide layers, linking chiral RVB states and spin fluctuations to superconductivity and novel metallic phases.

Findings

Chiral spin fluctuations enhance d-wave superconductivity at optimal doping.

A chiral RVB metal state with gauge field condensation is proposed.

Possible weak ferromagnetism and p-wave superconductivity at higher dopings.

Abstract

Takada et al. have reported superconductivity in layered $Na__x CoO_2.yH_2O$ ($T_c \approx5 K$) and more recently Wen et al. in $A_xCoO_{2+\delta}$ ($A = Na,K$)(\tc$\approx~31 K$). We model a reference neutral \cob layer as an orbitally non-degenerate spin-\half antiferromagnetic Mott insulator on a triangular lattice and $Na__x CoO_2.yH_2O$ and $A_xCoO_{2+\delta}$ 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 leads to a d-wave superconducting state. A chiral RVB metal, a PT violating state with condensed RVB gauge fields, with a possible weak ferromagnetism and low temperature p-wave superconductivity are also suggested at higher dopings.