Polaritonic Smith-Purcell radiations in van der Waals materials

Manipulating polaritons in van der Waals (vdW) materials offers a unique platform for advancing nanophotonic applications and enhancing our comprehension of strong light-matter interactions. Here, two-dimensional (2D) polaritonic Smith-Purcell radiation (SPR) that arises from the interaction between grazing-incidence electron beams and vdW materials patterned with a grating structure is investigated. We demonstrate that both isotropic graphene plasmons and hyperbolic phonon polaritons in α-phase molybdenum trioxide (α-MoO₃) can be excited efficiently by incident electron beams. Moreover, by adjusting the grating periodicity while keeping the operation frequency constant, the emission direction of the resulting polaritons can be precisely tuned. Our modeling of SPR generation on the surface of 2D vdW materials not only reveals the feasibility of SPR in low-dimensional systems, but also provides a versatile approach for nanoscale manipulation of infrared light.