High resolution scanning tunneling microscope (STM) image of SrTiO$_3$(100)-$\sqrt{5}\times\sqrt{5}-R26.6^\circ$ surface

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. STM images with truly atomic resolution in filled states, which have never been reported, were successfully obtained. The atomic arrangement in $\sqrt{5}\times\sqrt{5}$ unit cell is clearly seen. It is currently assumed that Ti and its fourfold site O atoms were separately imaged with varying bias voltages, which indicates that TiO$_2$ plane is a basic plane of $\sqrt{5}\times\sqrt{5}$ surface superstructures. The dI/dV images simultaneously taken with topographic images were also obtained in filled states. Comparing our experimental results with the previous works, especially a theoretical study of O-vacancy model [1] and an experimental and theoretical study of Sr adatom model [2], possible structures on $\sqrt{5}\times\sqrt{5}$ surfaces will be discussed.\\[4pt] [1] Z. Fang and K Terakura, Surf. Sci. 470, L75(2000)\\[0pt] [2] T. Kubo and H. Nozoye, Phys. Rev. Lett. 86, 1801(2001)