Probing the Interfacial Symmetry Using Rotational Second-Harmonic Generation in Oxide Heterostructures

Transition metal oxide thin films and heterostructures have attracted remarkable and continuous attention due to the incredible variety of electronic and magnetic properties. A significant challenge remains: to directly measure the electronic properties of the buried interface. Rotational second-harmonic generation (RSHG) is a powerful nonlinear optical technique for probing electronic symmetry originating from broken symmetry at the interface. In this Article, we characterize the novel electronic properties at the buried interface due to the broken symmetry, using epitaxially grown high-quality La2/3Sr1/3MnO3 (LSMO) thin films on SrTiO3 (STO) (001) substrates. The RSHG data of LSMO/STO(001) heterostructures show a combination of isotropic and 4-fold patterns. The isotropic symmetry in the RSHG data originates from the LSMO surface. The unusual 4-fold anisotropy originates from the buried interface, indicating that the interface symmetry cannot be higher than C2. A possible structural model is presented, involving a tilt of the octahedra.