Complete d-Band Dispersion and the Mobile Fermion Scale in NaxCoO2

TL;DR

This study maps the complete d-band dispersion in sodium cobaltates using advanced photoelectron techniques, revealing a many-body quasiparticle band with a small Fermi scale and confirming the Luttinger theorem at low doping levels.

Contribution

It provides the first detailed imaging of the full d-band dispersion in sodium cobaltates, highlighting many-body effects and the small Fermi scale in these oxides.

Findings

Observation of hybridization gap anticrossing in the band structure

Identification of a small many-body Fermi scale (~0.25 eV)

Confirmation of the 2D Luttinger theorem at low doping

Abstract

We utilize fine-tuned polarization selection coupled with excitation-energy variation of photoelectron signal to image the \textit{complete d}-band dispersion relation in sodium cobaltates. A hybridization gap anticrossing is observed along the Brillouin zone corner and the full quasiparticle band is found to emerge as a many-body entity lacking a pure orbital polarization. At low dopings, the quasiparticle bandwidth (Fermion scale, many-body \textit{E$_F$} $\sim$ 0.25 eV) is found to be smaller than most known oxide metals. The low-lying density of states is found to be in agreement with bulk-sensitive thermodynamic measurements for nonmagnetic dopings where the 2D Luttinger theorem is also observed to be satisfied.