LOCAL LATTICE DISTORTIONS IN YBa2Cu3Oy PROBED BY XAS: CRITICAL FLUCTUATION, PSEUDOGAP OPENING AND STRIPE ORDERING

Abstract

Local lattice distortions in YBa 2 Cu 3 O y single crystals are studied by polarized x-ray absorption spectroscopy (XAS) for E//ab 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 Tl=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 transform shows that the lattice fluctuation are reduced below T2~ T*=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.