Local lattice instability and stripes in the CuO₂ plane of the La_1.85Sr_0.15CuO₄ system by polarized XANES and EXAFS

Temperature-dependent polarized Cu K-edge x-ray absorption has been used to investigate local structural distortions in the CuO₂ plane of the La_1.85Sr_0.15CuO₄ system. The Cu-O pair distribution shows the presence of a minority phase containing CuO₆ octahedra characterized by a shorter Cu-O(apical) bond (ΔR∼-0.1 Å) and two longer Cu-O(planar) bonds (ΔR∼+0.08 Å) and a tilting angle of 16°±2°. The temperature-dependent distortions show a maximum around T (∼1.6T_c) and a minimum at T_c (∼35 K). The data show the coexistence of two types of doped charges in different stripes in the superconducting phase.