Figure 7. Schematic plot of the band offset (top panels) and electronic reconstruction (bottom panels) that summarizes some of the important DFT results described in the text.

The left panels show results for LAO/STO, while GTO/STO results are shown on the right. Prior to electronic reconstruction in LAO/STO, the top of the valence band (VB) in LAO is widely separated in energy from the bottom of the conduction band (CB) in STO. Thus electronic reconstruction requires a large band bending, which is responsible for the threshold in LAO thickness for the polar catastrophe to set in. In contrast, the VB in GTO is the Ti-d lower Hubbard band, which is already close in energy to the CB in STO prior to reconstruction. Thus only a modest band-bending is required for a conduction electron density of 0.5e per interface Ti. We also see in the reconstructed GTO/STO electronic structure the charge gap due to the correlation-induced charge disproportionation in the top TiO₂ layer next to vacuum.