Local Lattice Anomalies in Epitaxial YBa_2Cu_3O_<7-δ> Thin Film Studied by X-Ray Absorption Fine Structure

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The temperature dependence of the local structure in epitaxial YBa_2 Cu_3O_<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) simultaneously 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.
社団法人日本物理学会の論文
1995-07-15