A Tight-Binding Investigation of the NaxCoO2 Fermi Surface

TL;DR

This paper uses tight-binding models fitted to first-principles calculations to analyze how the Fermi surface of Na$_x$CoO$_2$ evolves with doping, revealing persistent small hole pockets and their dependence on oxygen height.

Contribution

It provides a detailed tight-binding analysis of Na$_x$CoO$_2$'s Fermi surface and clarifies the role of oxygen position in its electronic structure.

Findings

Small e$_{g'}$ hole pockets are preserved across dopings.

Fermi surface features depend on oxygen height.

Possible reasons for missing experimental evidence for these pockets.

Abstract

We perform an orthogonal basis tight binding fit to an LAPW calculation of paramagnetic Na$_x$CoO$_2$ for several dopings. The optimal position of the apical oxygen at each doping is resolved, revealing a non-trivial dependence of the band structure and Fermi surface on oxygen height. We find that the small e$_{g'}$ hole pockets are preserved throughout all investigated dopings and discuss some possible reasons for the lack of experimental evidence for these Fermi sheets.