Dynamical mean field theory of an effective three-band model for Na$_x$CoO$_2$

TL;DR

This paper develops an effective three-band model for Na$_x$CoO$_2$ and solves it using dynamical mean-field theory, successfully reproducing experimental Fermi surfaces and explaining doping-dependent features.

Contribution

It introduces a new effective Hamiltonian for Na$_x$CoO$_2$ based on multi-orbital cluster solutions and applies DMFT to match experimental observations.

Findings

Fermi surface and dispersion agree with ARPES data

Explains the origin of sinking pockets in doping regimes

Provides insights into the electronic structure of Na$_x$CoO$_2$

Abstract

We derive an effective Hamiltonian for highly correlated $t_{2g}$ states centered at the Co sites of Na$_x$CoO$_2$. The essential ingredients of the model are an O mediated hopping, a trigonal crystal-field splitting, and on-site effective interactions derived from the exact solution of a multi-orbital model in a CoO$_6$ cluster, with parameters determined previously. The effective model is solved by dynamical mean-field theory (DMFT). We obtain a Fermi surface (FS) and electronic dispersion that agrees well with angle-resolved photoemission spectra (ARPES). Our results also elucidate the origin of the "sinking-pockets" in different doping regimes.