Evidence for charge-density-wave nature of the charge-ordered phase inLa1/3Sr2/3FeO3

Abstract

We have investigated the threefold-charge ordering in ${\text{La}}_{1/3}{\text{Sr}}_{2/3}{\text{FeO}}_{3}$ sample below ${T}_{\text{CO}}$ $\ensuremath{\sim}200\text{ }\text{K}$. We have measured superlattice reflections, $q={a}^{\ensuremath{\ast}}(1/3\text{ }1/3\text{ }1/3)$, using the resonant x-ray scattering technique. The nonresonant intensities are consistent with a periodic structural modulation of both Fe and $\text{Sr}(\text{La}){\text{O}}_{3}$ atomic planes. These displacements give rise to two nonequivalent Fe sites in the ratio of 2:1. Strong resonances are observed at the $\text{Fe}\text{ }K$ edge in the $\ensuremath{\sigma}\text{\ensuremath{-}}{\ensuremath{\sigma}}^{\ensuremath{'}}$ geometry. These resonances did not exhibit azimuthal dependence. A charge disproportionation of 0.6 electrons is determined between the two Fe sites. Hence, the charge-ordered phase can be better understood as a charge-density-wave with a $\dots{}{\text{Fe}}^{3.3+}{\text{Fe}}^{3.9+}{\text{Fe}}^{3.9+}\dots{}$ sequence along the cubic [111] direction.