A unified origin for the 3D magnetism and superconductivity in Na$_x$CoO$_2$

TL;DR

This paper proposes that the 3D magnetism and superconductivity in Na$_x$CoO$_2$ originate from the same Fermi surface nesting mechanism, linking magnetic order and superconducting fluctuations in a unified framework.

Contribution

It introduces a 3D Hubbard model analysis showing that Fermi surface nesting causes 3D magnetism and links it to superconductivity in Na$_x$CoO$_2$.

Findings

Fermi surface nesting explains 3D magnetism.

Calculated spin wave dispersion matches neutron scattering data.

Magnetism and superconductivity share a common origin.

Abstract

We analyze the origin of the three dimensional (3D) magnetism observed in nonhydrated Na-rich Na$_x$CoO$_2$ within an itinerant spin picture using a 3D Hubbard model. The origin is identified as the 3D nesting between the inner and outer portions of the Fermi surface, which arise due to the local minimum structure of the $a_{1g}$ band at the $\Gamma$-A line. The calculated spin wave dispersion strikingly resembles the neutron scattering result. We argue that this 3D magnetism and the spin fluctuations responsible for superconductivity in the hydrated systems share essentially the same origin.