Intrinsic origin of interface states and band-offset profiling of nanostructured LaAlO3/SrTiO3 heterojunctions probed by element-specific resonant spectroscopies

The origin of electronic states at the basis of the 2DEG found in conducting LaAlO3/SrTiO3 interfaces (5 u.c. LaAlO3) is investigated by resonant photoemission experiments at the Ti L2,3 and La M4,5 edges. As shown by the resonant enhancement at the Ti L2,3 edge, electronic states at EF receive a dominant contribution from Ti 3d states. Both Ti and La resonance effects in the valence-band region are used to estimate the valence-band maxima at the two sides of the junction. Through a comparison with the valence-band states of the LaAlO3 and SrTiO3 parent compounds, we reconstruct the band diagram of the heterojunction, which is revealed to be type I (straddling gap), with a large notch of the band profile at the interface as compared with the reference insulating (3 u.c. LaAlO3) interface.