The conducting interface of LaAlO3/SrTiO3 heterostructures has been studied by hard X-ray photoelectron spectroscopy. From the Ti 2p signal and its angle-dependence we derive that the thickness of the electron gas is much smaller than the probing depth of 4 nm and that the carrier densities vary with increasing number of LaAlO3 overlayers. Our results point to an electronic reconstruction in the LaAlO3 overlayer as the driving mechanism for the conducting interface and corroborate the recent interpretation of the superconducting ground state as being of the BerezinskiiKosterlitz-Thouless type.
We present a detailed study of the electronic structure and band alignment in LaAlO 3 /SrTiO 3 oxide heterostructures by hard x-ray photoelectron spectroscopy. Our spectroscopic measurements find no evidence for the strong potential gradient within the polar LaAlO 3 film predicted by band theory. Due to the high interface sensitivity of the method, we are further able to determine the valence band offset between the LaAlO 3 film and the SrTiO 3 substrate, which is found to be independent of the number of LAO overlayers. Finally, we discuss several explanations for the apparent absence of the built-in field in ex situ prepared LaAlO 3 /SrTiO 3 heterostructures.
We report the formation of a nonmagnetic band insulator at the isopolar interface between the antiferromagnetic Mott-Hubbard insulator LaTiO_{3} and the antiferromagnetic charge transfer insulator LaFeO_{3}. By density-functional theory calculations, we find that the formation of this interface state is driven by the combination of O band alignment and crystal field splitting energy of the t_{2g} and e_{g} bands. As a result of these two driving forces, the Fe 3d bands rearrange and electrons are transferred from Ti to Fe. This picture is supported by x-ray photoelectron spectroscopy, which confirms the rearrangement of the Fe 3d bands and reveals an unprecedented charge transfer up to 1.2±0.2 e^{-}/interface unit cell in our LaTiO_{3}/LaFeO_{3} heterostructures.
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