Lattice fluctuations and inhomogeneous charge states of high-Tc superconductors

Abstract

We have used x-ray absorption spectroscopy as a tool to study instantaneous local lattice distortions of the CuO2 plane in high-Tc superconductors and we have investigated the inhomogeneous charge states of these materials. The temperature-dependent Cu K-edge extended x-ray absorption fine structure (EXAFS) has been used to determine the correlated Debye–Waller factor of the Cu–O bonds, measuring local lattice fluctuations. The Debye–Waller factor of the Cu–O bonds shows an order-parameter-like behaviour across the charge stripe ordering temperature. The EXAFS results are supported by a temperature-dependent Cu K-edge x-ray absorption near edge structure (XANES) revealing a particular change in the local lattice displacements at the charge stripe ordering. The experimental Cu K-edge XANES results are well reproduced by full multiple scattering calculations including different distortions of the CuO2 plane showing particular lattice displacements which are consistent with the EXAFS results. The particular distortion mode as a response function to the charge stripe ordering has been discussed with several examples. The results are consistent with an inhomogeneous charge distribution in the high-Tc cuprates suggesting an intimate relationship between the charge stripe ordering, local lattice fluctuations and high-Tc superconductivity in the cuprates.