Lattice Anomalies in (La,Sr)2CuO4 Under Epitaxial Strain Probed by Polarized X-Ray Absorption Spectroscopy

Local lattice anomalies in optimally doped T-(La,Sr)2CuO4 single crystal like thin films (Tc = 43.4 K) grown by molecular-beam epitaxy have been studied by the in-plane polarized Cu K-edge extended X-ray absorption fine structure (EXAFS). The results indicate temperature-dependent local atomic displacements which are anomalous at the Tc and below a higher temperature Ts as demonstrated by a change in the mean square relative displacement of the Cu–O bond \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sigma _{{\rm Cu}-{\rm O}}^2$$\end{document}, i.e., a sharp drop at the Tc and a gradual deviation from a noncorrelated Debye-like behavior below Ts where the spatial inhomogeneity appears. We find that the magnitude of the Cu–O displacement changes at the Tc, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta \sigma _{{\rm Cu}-{\rm O}}^2$$\end{document} is enhanced by compressive strain while the tendency of charge segregation is suppressed. The results suggest that the uniaxial pressure effects stabilize the system by decreasing the onset temperature and magnitude of spatial heterogeneity.