High resolution STM imaging of a unit cell of SrTiO$_3$(100)-$\sqrt{5}\times\sqrt{5}-R26.6^\circ$ surface superstructures

SrTiO$_3$(100)-$\sqrt{5}\times\sqrt{5}-R26.6^\circ$ surfaces were studied by scanning tunneling microscope (STM) in ultra-high vacuum conditions at room temperatures. In the our previous report, we showed the arrangement of titanium and oxygen atoms in the unit cells of a ($\sqrt{5}\times\sqrt{5}$) surface superstructure with scanning tunneling microscope and concluded the TiO$_2$ layer is the terminating plane of the ($\sqrt{5}\times\sqrt{5}$) surface [1]. Recently, we succeeded in imaging the surfaces in filled states with much higher spatial resolution. Oxygen atomic orbitals are individually recognized and the local structures at the center of the O fourfold hollow site with ($\sqrt{5}\times\sqrt{5}$) periodicity are more clearly seen. Comparing our experimental results with the previous works, especially a theoretical study of O-vacancy model [2] and an experimental and theoretical study of Sr adatom model [3], detailed discussion on $\sqrt{5}\times\sqrt{5}$ surfaces became possible.\\[4pt] [1] I. Shiraki and K. Miki, Surf. Sci. 605, 1304(2011)\\[0pt] [2] Z. Fang and K Terakura, Surf. Sci. 470, L75(2000)\\[0pt] [3] T. Kubo and H. Nozoye, Phys. Rev. Lett. 86, 1801(2001)