LaAlO3/SrTiO3 oxide heterostructures studied by resonant inelastic x-ray scattering

We report the application of resonant inelastic x-ray scattering to explore the nature of the single conducting interface in the oxide heterostructure LaAlO3/SrTiO3. From the Ti 3d crystal-field excitations measured at the Ti L-3 resonance we not only derive information on the local geometry at the interface but are also able to follow the evolution of the sheet carrier density with the thickness of the LaAlO3 overlayer. These findings confirm after calibration to previous hard x-ray photoelectron spectroscopy measurements that the charge density from spectroscopy exceeds the one derived from Hall-effect measurements, indicating the coexistence of itinerant and localized Ti 3d electrons at the interface. On the other hand, we observe a saturation of the charge-carrier concentration above a LaAlO3 thickness of 6 unit cells at similar to 1 x 10(14) cm(-2), well below the canonical value for ideal electronic reconstruction.