Enhancement of the superconducting critical temperature of Sr2CuO3+δ up to 95 K by ordering dopant atoms

We address the question of whether the superconducting transition temperature (T-c) of high-T-c cuprates is enhanced when randomly distributed dopant atoms form an ordered array in the charge reservoir layers. This study is possible for the Sr2CuO3+delta superconductor with K2NiF4-type structure in which oxygen atoms only partially occupy the apical sites next to the CuO2 planes and act as hole dopants. We show that remarkable T-c enhancement up to 95 K in this mono CuO2 layered high-temperature cuprate superconductor (HTS) is associated with the apical oxygen ordering, not to the hole concentration change. The result points a route toward further enhancement of T-c in cuprate superconductors.