Experimental Evidences for Static Charge Density Waves in Iron   Oxy-pnictides
  In this Letter we report high-resolution synchrotron X-ray powder diffraction and transmission electron microscope analysis of Mn-substituted LaFeAsO samples, demonstrating that a static incommensurate modulated structure develops across the low-temperature orthorhombic phase, whose modulation wave-vector depends on the Mn content. The incommensurate structural distortion is likely originating from a charge-density-wave instability, a periodic modulation of the density of conduction electrons associated with a modulation of the atomic positions. Our results add a new component in the physics of Fe-based superconductors, indicating that the density wave ordering is charge-driven. 
A. Martinelli, P. Manfrinetti, A. Provino, A. Genovese, F. Caglieris,   G. Lamura, C. Ritter, M. Putti
cond-mat.supr-con