Tunable Metallicity of the La5/8Ca3/8MnO3(001) Surface by an Oxygen Overlayer

We studied the surface structure of La5/8Ca3/8MnO3(001) thin films using in situ scanning tunneling microscopy (STM). Atomically resolved STM images reveal that a (root 2 X root 2)R45 degrees reconstructed surface and a (1 X 1) surface can be converted back and forth through adsorption and desorption of oxygen at the surface. The electrical properties of the surfaces are investigated by scanning tunneling spectroscopy. I - V curves clearly show that the presence of an oxygen overlayer renders the surface insulating while the (1 X 1) surface without the oxygen overlayer is metallic.