Role of electronic correlations in the Fermi surface formation of Na$_x$CoO$_2$

TL;DR

This study investigates how electronic correlations influence the Fermi surface in Na$_x$CoO$_2$, showing that correlations suppress certain hole pockets and reduce bilayer splitting, aligning with experimental observations.

Contribution

It demonstrates the significant role of electronic correlations in shaping the Fermi surface and bilayer splitting in Na$_x$CoO$_2$, using LDA+U and Gutzwiller methods.

Findings

Suppression of $e'_g$ hole pockets due to correlations

Reduction of bilayer splitting in Gutzwiller approximation

High spin state formation in Co is unlikely

Abstract

Band structure of metallic sodium cobaltate Na$_x$CoO$_2$ ($x$=0.33, 0.48, 0.61 0.72) has been investigated by local density approximation+Hubbard $U$ (LDA+$U$) method and within Gutzwiller approximation for the Co-$t_{2g}$ manifold. Correlation effects being taken into account results in suppression of the $e'_g$ hole pockets at the Fermi surface in agreement with recent angle-resolved photo-emission spectroscopy (ARPES) experiments. In the Gutzwiller approximation the bilayer splitting is significantly reduced due to the correlation effects. The formation of high spin (HS) state in Co $d$-shell was shown to be very improbable.