Micro-Strain and Self Organization of Localized Charges in Copper Oxides

It has been recently shown that local lattice distortions in complex oxides are intimately related with the micro-strain in the electronically active structural element, as the CuO₂ plane of doped copper oxide superconductors. In fact, the microstrain of the Cu-O bond controls the electron-lattice interaction. Here we have investigated charge ordering in an oxygen doped La₂CuO_4.1 crystal by high-resolution x-ray diffraction using synchrotron radiation. Thanks to the high brilliance synchrotron radiation it has been possible to record a large number of weak superstructure spots due to charge ordering around the main peaks of the average structure. A study of the charge modulations with stage 3.5, and their behavior as a function of the intensity of the x-ray incident flux is reported. Using an approach based on joint x-ray photo-excitation and x-ray diffraction we are able to see the self organization of photo-doped charges into short range polaron striped bubbles (a 2D superstructure q₃) and a 3D polaron crystal of strings (a 3D superstructure q₄).