Charge-ordering, commensurability and metallicity in the phase diagram of layered Na(x)CoO(2)

TL;DR

This study maps the phase diagram of layered Na(x)CoO(2), revealing how varying sodium content induces transitions from metallic to insulating and magnetically ordered states, highlighting charge-ordering and Na-ion coupling effects.

Contribution

It provides a detailed phase diagram of Na(x)CoO(2) with new insights into charge-ordering, commensurability, and their impact on metallicity and magnetic properties.

Findings

Transition from paramagnetic metal to charge-ordered insulator at x=1/2

Identification of a Curie-Weiss metal around x=0.70

Observation of weak-moment magnetic order for x>0.75

Abstract

The phase diagram of non-hydrated Na(x)CoO(2) has been determined by changing the Na content x using a series of chemical reactions. As x increases from 0.3, the ground state goes from a paramagnetic metal to a charge-ordered insulator (at x=1/2) to a `Curie-Weiss metal' (around 0.70), and finally to a weak-moment magnetically ordered state (x>0.75). The unusual properties of the state at 1/2 (including particle-hole symmetry at low T and enhanced thermal conductivity) are described. The strong coupling between the Na ions and the holes is emphasized.