Nonlinear Optical Response of SrTiO3/LaAlO3 Superlattices

The electronic symmetry of the SrTiO3/LaAlO3 interface was investigated by optical second harmonic generation, using superlattices with varying periodicity to study the evolution of the electronic reconstruction while avoiding substrate contributions. The superlattices show large perpendicular optical nonlinearity, which abruptly increases when the sublattice thickness goes above 3 unit cells, revealing substantial effects of the polar-nonpolar interface. The nonlinear 'active' area is primarily in SrTiO3, develops with increasing thickness, and extends up to 8 unit cells from the interface.