Electronic structure of the hydrogen-adsorbed SrTiO₃(001) surface studied by polarization-dependent photoemission spectroscopy

The metallic band structure of the hydrogen-adsorbed SrTiO₃(001) surface is studied by polarization-dependent photoemission spectroscopy measurements. With the dipole-transition selection arguments, we attributed the metallic peaks into the Ti 3d_xz, 3d_yz, and 3d_xy bands. These t_2g bands are partially filled with electrons upon H-induced downward band bending at the surface. Energy splitting of the Ti 3d t_2g bands is considered to be induced by a quantum confinement along the surface normal (z) direction. The metallic peaks are accompanied by the incoherent states induced by many-body interactions, which likely indicates that the electronic system forms a two-dimensional liquid phase. Also emerged by H exposure are an in-gap state and a σ(O-H) state. The possible origin and the feature of these states are discussed from the polarization dependence of the photoemission intensity.