Temperature dependence of the local structure in superconducting and non-superconducting Tl 2Ba 2CuO y studied by extended x-ray absorption fine structure

Abstract

The local structure of Tl 2Ba 2CuO y (Tl2201) has been investigated by extended X-ray absorption fine structure (EXAFS) on the Cu K-edge. The result for the high- T c sample with T c =70 K indicates a splitting of Cu-O bondlengths in the CuO 2 plane, which shows a strong temperature dependence over a wide temperature range well above T c, although the crystallographical symmetry of the unit cell is tetragonal. The splitting is evaluated from the filtered EXAFS by the beat-node method, and the maximum splitting distance is ≁0.16 Å. The magnitude of the splitting abruptly decreases in the vicinity of T c by more than 10%. On the other hand, no splitting in the in-plane Cu-O bondlengths was observed in non-superconductor samples from room temperature down to 30 K. No apparent change of axial oxygen sites was observed. These facts strongly demonstrate that the local structural distortion in the CuO 2 plane may directly relate to the superconductivity.