Photoemission from Buried Interfaces in SrTiO3/LaTiO3 Superlattices

We have measured photoemission spectra of SrTiO₃/LaTiO₃ superlattices with a topmost SrTiO₃ layer of variable thickness. A finite coherent spectral weight with a clear Fermi cutoff was observed at chemically abrupt SrTiO₃/LaTiO₃ interfaces, indicating that an “electronic reconstruction” occurs at the interface between the Mott insulator LaTiO₃ and the band insulator SrTiO₃. For SrTiO₃/LaTiO₃ interfaces annealed at high temperatures (∼1000°C), which leads to Sr/La atomic interdiffusion and hence to the formation of La_1-xSr_xTiO₃-like material, the intensity of the incoherent part was found to be dramatically reduced whereas the coherent part with a sharp Fermi cutoff was enhanced due to the spread of charge. These important experimental features are well reproduced by layer dynamical-mean-field-theory calculation.