Atomic visualization of copper oxide structure in the infinite-layer cuprate SrCuO2

We report the atomic-scale structure of epitaxial films of the parent infinite-layer compound SrCuO2 prepared on SrTiO3 by molecular beam epitaxy. In situ scanning tunneling microscopy study reveals a stoichiometric copper oxide (CuO2) -terminated surface featured by 2 x 2 reconstruction, caused primarily by structural distortions of four adjacent CuO2 plaquettes. Furthermore, the subsurface Sr atoms have been rarely discernible, showing intra-unit-cell rotational symmetry breaking. These observations can be reasonably modeled by a periodic up-down buckling of oxygen ions on the CuO2 plane. Further postannealing leads to the removal of surface oxygens and an incommensurate stripe phase. Our study provides indispensable structural information to help understand the exotic properties of cuprate superconductors.