^{59}Co NMR evidence for charge ordering below T_{CO}\sim 51 K in Na_{0.5}CoO_2

TL;DR

This study provides clear $^{59}$Co NMR evidence that charge ordering occurs below approximately 51 K in Na$_{0.5}$CoO$_{2}$, leading to an insulating ground state in this sodium cobaltate compound.

Contribution

The paper presents the first direct NMR evidence of charge ordering in Na$_{0.5}$CoO$_{2}$ below 51 K, linking it to the transition to an insulating state.

Findings

Charge ordering occurs below 51 K.

Charge ordering induces the insulating ground state.

The magnetic transition occurs at 86 K.

Abstract

The CoO$_{2}$ layers in sodium-cobaltates Na$_{x}$CoO$_{2}$ may be viewed as a spin $S=1/2$ triangular-lattice doped with charge carriers. The underlying physics of the cobaltates is very similar to that of the high $T_{c}$ cuprates. We will present unequivocal $^{59}$Co NMR evidence that below $T_{CO}\sim51 K$, the insulating ground state of the itinerant antiferromagnet Na$_{0.5}$CoO$_{2}$ ($T_{N}\sim 86 K$) is induced by charge ordering.