  The local electronic structure of the SrO-terminated SrTiO3(001) surface was
explored using scanning tunneling microscopy. At low bias voltages in the empty
states, a unidirectional structure with a periodicity of 3 unit cells,
superimposed on a c(2 x 2) reconstructed structure, was found to develop along
the crystallographic a axis. This structure indicates a charge-ordered stripe
induced by carrier doping from oxygen vacancies in the SrO and the subsurface
TiO2 planes. In the filled states, localized deep in-gap states were observed
in addition to large energy gaps in the tunneling spectra. This result
represents inelastic tunneling due to significant electron-lattice interaction
associated with unidirectional lattice distortion in the SrO-terminated
surface.
