Real-Space Imaging of Orbital Selectivity on SrTiO(001) Surface.

Real-space access of the orbital degree of freedom in complex oxides is still challenging due to intricate electronic hybridization. Here, we report a direct observation of reproducible orbital-selective tunneling on a novel SrTiO(001) surface by scanning tunneling microscopy. The electronic structures reversibly switch between two different sets of symmetries depending on the sample bias, which is accompanied by a remarkable change in energy-dependent spectroscopy data. Tunneling spectrum combined with density functional theory calculations elucidates that symmetry-breaking at the surface determines the crystal-splitting field of e/t orbitals with a strong in-plane anisotropy so that electrons alternatingly fill e and t orbitals during the imaging process with different biases. This surface superstructure provides a new strategy toward understanding orbital textures and orbital selectivity in complex oxides.