paper

Effect of Na content and hydration on the excitation spectrum of the cobaltite Na_xCoO_2 yH_2O

arXiv:cond-mat/0309186 · doi:10.1088/0953-8984/16/11/041

Abstract

We report on a Raman scattering study on the superconducting cobaltite $N a_{x} C o O_{2} \cdot y H_{2} O$ as function of Na content and hydration (x $\approx$ 1/3, 3/4 and y $\approx$ 0, 2/3, 4/3). The observed phonon scattering and scattering continua are analyzed in terms of lattice strain due to the structural misfit and disorder. Hydration, due to the intercalation of one or two $H_{2} O$ layers, releases a part of this strain. Our Raman data suggest a connection between disorder on the partly occupied Na sites, the split off of the $a_{1 g}$ level from the other $t_{2 g}$ states of $C o^{4 +}$ and superconductivity.

10 pages, 4 figures, for further information see http://www.peter-lemmens.de