Local lattice distortions in YBa2Cu3Oy probed by XAS: critical fluctuation, pseudogap opening and stripe ordering

Local lattice distortions in YBa2Cu3Oy single crystals are studied by polarized x-ray absorption spectroscopy (XAS) for E/lab and E//c orientations between 300 K and 20 K. From the Fourier transform analysis of the Cu K-EXAFS oscillations, we find that the out-of-plane Cu-O correlation shows an anomalous temperature dependence of radial distribution below T-1=240-250 K, indicating an increase of lattice fluctuations, while no anomalies are found for the Cu-Ba correlation. On further lowering temperature, the Fourier transfom shows that the lattice fluctuation are reduced below T(2)similar toT*=140-150 K associated with pseudogap opening. Below T*, the radial distribution of oxygen atoms became asymmetric, indicating that the distorted domain is formed. A strong electron-lattice coupling is indicated by the anomalous local lattice distortions at the cross-over temperatures characterizing various electronic transitions in the title system.