Leaky Waves in Flatland

We introduce a new in-plane radiation mechanism that can occur in artificial or natural low-dimensional materials, which can be viewed as the "flatland" analog of conventional leaky-wave radiation. We show that this concept can be physically realized in suitably designed planar junctions of purely reactive, isotropic metasurfaces supporting line waves. Our results provide a new tool for manipulating surface waves, which can find interesting applications in the emerging field of van der Waals polaritonics.