Local structure study of T′ cuprate superconductors

Undoped T′-type cuprates are believed to be charge transfer (Mott–Hubbard) insulators. Recent observation of undoped superconducting T′-type cuprates suggests half-filling weakly correlated metallic electron states (Tsukada et al.), which is against the fundamental picture. Here we report the local structures of undoped T′-(La3+,Y3+)2CuO4 and doped T′-(La3+,Ce4+)2CuO4 thin-film single crystals by polarized extended X-ray absorption fine structure (EXAS). The in-plane (E//ab) polarized Cu K-EXAFS data shows a remarkable Cu–O bond distance displacement. The broadened Cu–O distribution suggests a large local lattice distortion in T′-type structures, which might influence the electronic structure.