Second harmonic generation in AB-type LaTiO3/SrTiO3 superlattices

We report the generation and control of second harmonic generation (SHG) from a series of LaTiO3/SrTiO3 superlattices. We demonstrate that the nonlinear optical susceptibility χ(2) and the SHG pattern can be tuned by tailoring the number of superlattice interfaces. Significantly, unlike the conventional ABC-type nanostructures, our AB-type nanostructures can also produce SHG signals. The χ(2) value (24.3 pm/V) is even one to two orders of magnitude greater than the conventional ones. Hence, we demonstrate that SHG is a local microscopic process—it does not rely on macroscopic broken inversion symmetry. Moreover, we show that temperature dependence or structural phase transition can further enhance the SHG intensity. Our results introduce a scheme for SHG, extending the generation and control of SHG in nano-photonics to nearly all the accessible centrosymmetric materials.