BaTiO3(001)-(2×1): surface structure and spin density.

Using surface x-ray diffraction and ab initio calculations we present a model of the BaTiO3(001)-(2×1) surface structure, which has not been considered so far. While the crystal is terminated by two TiO2 layers similarly to SrTiO3(001)-(2×1), we find that one out of two surface layer Ti-atoms resides in a tetragonal pyramidal oxygen environment. This peculiar geometry leads to a metallic and magnetic surface involving local magnetic moments up to 2μ(B) in magnitude located at surface Ti and O atoms. Our results are important for the understanding of the intrinsic surface metallicity of insulating oxides in general.