Evidence for Polar Symmetry Coupling at MoS$_2$/Ferroelectric Heterointerfaces.

The complex oxide heterointerfaces and van der Waals (vdW) heterostructures present two versatile platforms for exploring emergent quantum phenomena and designing new functionalities. The rich opportunity offered by the synergy between complex oxides and vdW materials, however, is yet to be charted. In this work, we report the nonlinear optical signature of the polar coupling between monolayer MoS$_2$ and a neighboring ferroelectric oxide thin film. The interfacial second harmonic generation response can be substantially enhanced or almost entirely quenched by the domain walls or polar domains in the ferroelectric. Unlike the extensively studied coupling mechanisms driven by charge, spin, and lattice, this unconventional optical filtering effect is solely mediated by the interfacial polar symmetry, pointing to a new material strategy for the functional design of nanoscale reconfigurable optical applications.