Spatially Resolved Nano-Scale Characterization of Electronic States in SrTiO$_3$(001) Surfaces by STM/STS

We have performed low temperature scanning tunneling microscopy/spectroscopy (STM/STS) measurements on TiO$_2$-terminated SrTiO$_3$(001) thin film surfaces. The conductance map exhibited electronic modulations that were completely different from the surface structure. We also found that the electronic modulations were strongly dependent on temperature and the density of atomic defects associated with oxygen vacancies. These results suggest the existence of strongly correlated two-dimensional electronic states near the SrTiO$_3$ surface, implying the importance of electron correlation at the interfaces of SrTiO$_3$-related heterostructures.