Enhanced lattice polarization in SrTiO3/LaAlO3 superlattices measured using optical second-harmonic generation

Lattice polarization at the SrTiO3/LaAlO3 interface was investigated by optical second harmonic generation. Superlattices with varying periodicity were employed to study the evolution of interface polarization, while separating substrate contributions. We observed large perpendicular optical nonlinearity, which abruptly increases when the sublattice thickness goes above 3 unit cells. The polarization is primarily in SrTiO3 and develops up to 8 unit cells from the interface.