Topological frequency conversion in rhombohedral graphene multilayers

We investigate the phenomenon of topological frequency conversion -- characterized by a quantized rate of energy transfer between two monochromatic light sources -- in two-dimensional materials. We focus on rhombohedral graphene multilayers, which are promising candidates to realize this effect due to the Berry curvature of their low-energy bands which can be controlled by a perpendicular electric field. We find a topological conversion efficiency that is frequency independent and of order αL with α the fine structure constant and L the number of layers. We then discuss the important role of light polarization, highlighting potential cancellations between valleys, and comment on dissipation effects.