Tunable metallicity of the La5/8Ca3/8MnO3(001) surface by an oxygen overlayer.

We studied the surface structure of La_{5/8}Ca_{3/8}MnO_{3}(001) thin films using in situ scanning tunneling microscopy (STM). Atomically resolved STM images reveal that a (sqrt[2]xsqrt[2])R45;{ degrees } reconstructed surface and a (1x1) 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 (1x1) surface without the oxygen overlayer is metallic.