Atomic-scale structure of a SrTiO3 bicrystal boundary studied by scanning tunneling microscopy

An atomically flat and well ordered c(6 X 2)(001) surface of a [100] tilted (2 X 12 degrees) artificial SrTiO3 bicrystal was prepared by thermal annealing in oxygen and ultrahigh vacuum, and characterized with low-energy electron diffraction and scanning tunneling microscopy. The real-space images of the boundary show that the bicrystal boundary is not straight, but zigzagged along the [100] and [010] crystal axis, and grooved with a depth of several atomic steps down: to the bulk. We attribute the observed boundary structure to strong thermal etching-and crystal faceting effects. A simple model is proposed for the path of superconducting currents of high-T-c thin films crossing such a bicrystal boundary. The model yields a 1/tan(theta) dependence of the critical current crossing the bicrystal boundary, which explains very well the reported experimental data.