Electronic Correlations in CoO2, the Parent Compound of Triangular Cobaltates

TL;DR

This study uses 59Co NMR to investigate CoO2, revealing a metallic state with strong electron correlations and spin fluctuations, suggesting proximity to a Mott transition as sodium content decreases.

Contribution

It provides new insights into the electronic correlations and spin dynamics in CoO2, the parent compound of triangular cobaltates, highlighting its proximity to a Mott transition.

Findings

CoO2 exhibits a metallic ground state with strong electron correlations.

Low-energy spin fluctuations develop at specific wave vectors.

Electronic correlations increase as sodium content decreases below 0.3.

Abstract

A 59Co NMR study of CoO2, the x=0 end member of AxCoO2 (A = Na, Li...) cobaltates, reveals a metallic ground state, though with clear signs of strong electron correlations: low-energy spin fluctuations develop at wave vectors q different from 0 and a crossover to a Fermi-liquid regime occurs below a characteristic temperature T*~7 K. Despite some uncertainty over the exact cobalt oxidation state n this material, the results show that electronic correlations are revealed as x is reduced below 0.3. The data are consistent with NaxCoO2 being close to the Mott transition in the x -> 0 limit.