Measurement of electron correlations in LixCoO2 (x=0.0 - 0.35) using 59Co nuclear magnetic resonance and nuclear quadrupole resonance techniques

TL;DR

This study uses 59Co NMR and NQR to investigate electron correlations in LixCoO2, revealing that CoO2 is a non-correlated metal with three-dimensional structure, contrasting with the two-dimensional layered A_xCoO_2 compounds.

Contribution

It provides the first detailed NMR/NQR analysis of LixCoO2 across different x values, clarifying the electronic state and spin correlations in this series.

Findings

CoO2 is a non-correlated metal satisfying the Fermi liquid behavior.

Antiferromagnetic correlations increase as Li content decreases.

CoO2's three-dimensional structure explains the lack of electron correlations.

Abstract

CoO2 is the parent compound for the superconductor NaxCoO2\cdot1.3H2O and was widely believed to be a Mott insulator. We performed 59Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies on LixCoO2 (x = 0.35, 0.25, 0.12, and 0.0) to uncover the electronic state and spin correlations in this series of compounds which was recently obtained through electrochemical de-intercalation of Li from pristine LiCoO2. We find that although the antiferromagnetic spin correlations systematically increase with decreasing Li-content (x), the end member, CoO2 is a non-correlated metal that well satisfies the Korringa relation for a Fermi liquid. Thus, CoO2 is not simply located at the limit of x->0 for AxCoO2 (A = Li, Na) compounds. The disappearance of the electron correlations in CoO2 is due to the three dimensionality of the compound which is in contrast to the highly two dimensional structure of AxCoO2.