Direct observation of 1-dimensional charge order below the first-order "metal-insulator" transition in Yb₄As₃

Resonant X-ray diffraction results on the Yb L₃ absorption edge of Yb₄As₃ are reported. The strong enhancement at the absorption edge of reflections of type 303̄ at temperatures below the first-order phase transition is viewed as direct evidence of a 1-dimerisional charge order. The quantitative determination of the charge ordering, which does not follow the structural distortion, has direct impact on models describing the unusual electronic and magnetic properties of this material.