Spin-Dynamics in the Carrier-Doped $S=1/2$ Triangular-Lattice of Na$_{x}$CoO$_{2}$-yH$_{2}$O

TL;DR

This study investigates the local electronic and spin properties of Na$_x$CoO$_2$-yH$_2$O using 59-Co NMR, revealing distinct Co site behaviors and Fermi-liquid emergence at specific doping levels.

Contribution

It provides new insights into how carrier concentration affects local electronic states and spin fluctuations in the triangular-lattice cobaltate.

Findings

Two distinct Co site types for x>=1/2

Valence averaging at x~1/3

Fermi-liquid behavior below 100 K at x~1/3

Abstract

We probed the local electronic properties of the mixed-valent Co(+4-x) triangular-lattice in Na{x}CoO{2}-yH{2}O by 59-Co NMR. We observed two distinct types of Co sites for x>=1/2, but the valence seems averaged out for x~1/3. Local spin fluctuations exhibit qualitatively the same trend down to ~100 K regardless of the carrier-concentration x, and hence the nature of the electronic ground state. A canonical Fermi-liquid behavior emerges below ~100 K only for x~1/3.