Spatial inhomogeneities at the LaAlO3/SrTiO3 interface: Evidence from second harmonic generation

Phase-sensitive, spatially resolved optical second-harmonic-generation experiments were performed on LaAlO3/SrTiO3 heterostructures. Lateral inhomogeneities on a length scale of ≈ 30 μm are found when a one-unit-cell-thick epitaxial monolayer of LaAlO3 is grown on TiO2-terminated SrTiO3 single crystals. The inhomogeneity is absent in samples with LaAlO3 layers of more than one unit cell. The results are discussed in the framework of electronic, oxidic, and chemical inhomogeneities.