Local Lattice Anomalies in Epitaxial YBa2Cu3O7-δThin Film Studied by X-Ray Absorption Fine Structure

Abstract

The temperature dependence of the local structure in epitaxial YBa 2 Cu 3 O 7-δ thin film has been studied by polarized extended X-ray absorption fine structure (EXAFS) on the Cu K-edge. The results suggest that the local lattice anomalies occur not only at T c but also well above T c . The mean-square relative displacements for the two out-of-plane Cu–O bonds (Cu1–O4, Cu2–O4) s i m u l t a n e o u s l y increased at T c . The in-plane Cu–O bonds showed the anomalous decrease of dynamical disorder below 120 K ∼1.5 T c followed by a sharp increase at T c which saturates at lower temperature, consistent with other lattice anomalies or dynamical spin susceptibilities observed at ∼1.5 T c . These suggest that the anomaly in in-plane oxygen atom vibrations below 1.5 T c is caused by the coupling between lattice distortions and magnetic excitations. The correlated displacement of apical oxygen atoms may induce a bilayer coupling associated with a charge transfer.