  We have measured photoemission spectra of SrTiO3/LaTiO3 superlattices with a
topmost SrTiO3 layer of variable thickness. Finite coherent spectral weight
with a clear Fermi cut-off 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 La1-xSrxTiO3-like
material, the intensity of the incoherent part was found to be dramatically
reduced whereas the coherent part with a sharp Fermi cut-off is enhanced due to
the spread of charge. These important experimental features are well reproduced
by layer dynamical-mean-field-theory calculation.
