Robust Ti4+ states in SrTiO3 layers of La0.6Sr0.4MnO3/SrTiO3/   La0.6Sr0.4MnO3 junctions
  We have investigated the interfacial electronic structure of La0.6Sr0.4MnO3 (LSMO)/ SrTiO3 (STO)/ LSMO heterojunctions utilizing the elemental selectivity of photoemission spectroscopy. The Ti 2p core-level spectra clearly show Ti4+ states and do not exhibit any indication of Ti3+ states in TiO2 layers irrespective of a different kind of adjacent atomic layer with different chemical carrier concentration. This result indicates that the Ti ions in the TiO2 atomic layers preserve their tetravalent states even in the vicinity of the valence-mismatched interface between LSMO and STO, reflecting chemical stability of the Ti4+ states. 
H. Kumigashira, A. Chikamatsu, R. Hashimoto, M. Oshima, T. Ohnishi, M.   Lippmaa, H. Wadati, A. Fujimori, K. Ono, M. Kawasak...