Ferroelectric and multiferroic materials having the spontaneous polarization are usually very strong sources of the SHG signal, and hence relevant phase transitions can be easily traced by characterizing the magnitude and the direction of order parameters.
Currently, we are focusing on ferroelectricity or multiferroicity emerging in oxide thin films and van der Waals materials in their atomically thin limits.
Inversion symmetry is naturally broken at the interface and surface of any media which hence can be another strong source of the SHG signal.
This provide us with a valuable opportunity for the symmetry characterization of interface and surface states.
We are now examining structural reconstructions of single-layer or superlattice thin films at their interfaces/surface, expecting that this information will serve as a basis for deeper understanding of complicated but novel phenomena emerging at interface/surface.