Polar-discontinuity-retaining A-site intermixing and vacancies at SrTiO3/LaAlO3 interfaces

Our anomalous surface x-ray diffraction study of the interface between SrTiO3(001) substrates and thin polar films of LaAlO3 shows La/Sr interdiffusion leading to neutrally charged Sr1-1.5xLaxO layers. From a thickness of two unit cells, the LaAlO3 film's interior retains its polar stacking sequence, which is compensated by a cationic compositional change of the substrate's terminating TiO2 layer. While such valence-retaining A-site intermixing does not resolve the polar catastrophe, it may be a general feature at oxide interfaces influencing the electronic and magnetic properties.