Phase Diagram of Na$_x$CoO$_2$ Studied by Gutzwiller Density Functional Theory

TL;DR

This study uses an ab-initio Gutzwiller density functional approach to map the phase diagram of Na$_x$CoO$_2$, revealing distinct magnetic and electronic phases across different sodium concentrations.

Contribution

It provides a parameter-free, self-consistent characterization of the phase diagram of Na$_x$CoO$_2$ using the LDA+Gutzwiller method, improving upon previous parameter-dependent studies.

Findings

Identified a Stoner magnetic metal phase for x>0.6.

Discovered a correlated non-magnetic metal phase for 0.3<x<0.6.

Revealed the emergence of $e_g^{\

Abstract

The ground states of Na$_x$CoO$_2$ ($0.0<x<1.0$) is studied by the LDA+Gutzwiller approach, where charge transfer and orbital fluctuations are all self-consistently treated {\it ab-initio}. In contrast to previous studies, which are parameter-dependent, we characterized the phase diagram as: (1) Stoner magnetic metal for $x>0.6$ due to $a_{1g}$ van-Hove singularity near band top; (2) correlated non-magnetic metal without $e_g^{\prime}$ pockets for $0.3<x<0.6$; (3) $e_g^{\prime}$ pockets appear for $x<0.3$, and additional magnetic instability involves. Experimental quasi-particle properties is well explained, and the $a_{1g}$-$e_g^{\prime}$ anti-crossing is attributed to spin-orbital coupling.