Lattice Instability in High-Temperature Superconducting Cuprates: Polarons Probed by EXAFS

Lattice instability in the planar Cu-O bond in high-temperature superconducting cuprates is probed by the Cu K-edge extended X-ray absorption fine structure (EXAFS). Refined temperature-dependent polarized EXAFS data for high-quality La1.85Sr0.15CuO4 (LSCO) single crystals grown by MBE and TSFZ methods are analyzed and compared with the transport properties. Temperature-dependent oxygen displacement shows a signature of bond splitting at T (*) and a sharp drop due to superconductivity coherence at T (c). Detailed analysis of the anomalous oxygen displacement demonstrates the Cu-O bond splitting, i.e., long and short bonds (Delta Ra parts per thousand 0.12 A...), which is in good agreement with the recent cluster calculation. The results indicate that the origin of pseudogap is related to the formation of charged dynamical lattice distortions (polarons) that are coexistent with metallic (superconducting) domains.