Local structure study of T′ cuprate superconductors

Abstract 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 ′-(La 3+ ,Y 3+ ) 2 CuO 4 and doped T ′-(La 3+ ,Ce 4+ ) 2 CuO 4 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.