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

Abstract

Local lattice anomalies in optimally doped T-(La,Sr)₂CuO₄ single crystal like thin films (T _c = 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 T _c and below a higher temperature T _s as demonstrated by a change in the mean square relative displacement of the Cu–O bond $\sigma _{{\rm Cu}-{\rm O}}^2$, i.e., a sharp drop at the T _c and a gradual deviation from a noncorrelated Debye-like behavior below T _s where the spatial inhomogeneity appears. We find that the magnitude of the Cu–O displacement changes at the T _c, $\Delta \sigma _{{\rm Cu}-{\rm O}}^2$ 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.