Superconductivity and scanning tunneling microscopy (STM) / spectroscopy (STS) of transition metal oxide artificial lattices

High T_c superconducting artificial lattices and superlattices have been constructed by a laser molecular beam epitaxy. Layer-by-layer growth method controlled by RHEED and STM is a promising method for the construction of these artificial lattices. Formation and properties of superconducting artificial lattices and super-conducting / ferromagnetic superlattices are presented as the typical examples. In order to investigate the electronic state of carrier doped strongly correlated electronic system, STS measurements have been performed on La_2–xSr_xCuO₄, La_2–xSr_xNiO₄, and La_1-xSr_xMnO₃ thin films. Based on the similarities and the differences between the STS spectra of the three types of the films, electronic states of the strongly correlated system are discussed.