Experimental control of the structure in SrCuO₂ ultrathin films

A two-dimensional (2D) CuO₂ plane is the basis for studying high-T_c superconducting cuprate. The formation of the CuO₂ plane in oxide thin films is limited by the strong electrostatic instability at the termination between the thin film and substrate. In this study, the ultrathin (1 - 20 uc) SrCuO₂ films were successfully grown on TiO₂-terminated SrTiO₃ substrates using pulsed laser deposition. The thickness-dependent structural transformation of the SrCuO₂ films was studied by polarized x-ray absorption spectroscopy (XAS) at the Cu L edge. XAS with theoretical calculations clearly distinguished chain-type structure and plane-type structure. XAS show that the out-of-plane spectral weight decreases as the number of layer increases. In the 7uc SrCuO₂ ultrathin films, XAS shows the same behavior as that of the infinite-layer sample.