Incommensurate Sinusoidal Oxygen Modulations in Layered Manganites La1-xSr1+xMnO4 (x ≥ 0.5)

We have studied the incommensurate-ordered phase in overdoped La0.4Sr1.6MnO4 by resonant x-ray diffraction at the Mn K edge. Weak resonant superlattice (h +/- 0.2 h +/- 0.2 0) and (h +/- 0.4 h +/- 0.4 0) reflections of the tetragonal structure were found below similar to 240 K. The energy, azimuth angle, and polarization dependencies of the resonant scattering have revealed sinusoidal modulations of the oxygen motions that are transverse and longitudinal to the tetragonal [110] direction. This result discards (Mn3+, Mn4+)-like stripe-type order but point to a charge-density-modulation picture.