Correlation effects on the doped triangular lattice in view of the physics of sodium-rich Na$_x$CoO$_2$

TL;DR

This paper investigates the correlation effects on the doped triangular lattice in sodium-rich Na$_x$CoO$_2$ using a cluster slave boson approach, revealing how nonlocal correlations influence magnetic tendencies and the Mott transition.

Contribution

It introduces a rotationally invariant slave boson method in a cellular cluster approach to include nonlocal correlations in the study of Na$_x$CoO$_2$'s physics.

Findings

Nonlocal correlations affect magnetic tendencies in Na$_x$CoO$_2$.

Transition from antiferromagnetic to ferromagnetic behavior with doping.

Insights into the Mott transition at half filling.

Abstract

The peculiar correlation effects on the triangular lattice are studied by means of the rotationally invariant slave boson method in a cellular cluster approach. Hence nonlocal correlations are included in a short-range regime. Their impact for the single-band Hubbard model is studied at half filling, i.e., on the Mott transition, and with doping. Using the realistic band structure of Na$_x$CoO$_2$, we may also shed light on the cobaltate physics for $x$$\ge$1/3, with the in-plane transition from antiferromagnetic tendencies towards the onset of ferromagnetism for a finite Hubbard $U$.