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Electrical generation of surface plasmon polaritons in plasmonic heterostructures

Surface plasmon polaritons (SPPs) can be understood as two-dimensional light confined to a conductor-dielectric interface via plasmonic excitations. While low-energy SPPs behave similarly to photons, higher-frequency SPPs resemble surface plasmons. Electrically generating mid-range SPPs is particularly challenging because it requires compensating for momentum mismatch, a process conventionally achieved through inelastic electron transport in nanostructures. Here, we theoretically demonstrate that electrical SPP generation is possible by directly coupling electron-hole dipoles to the quantized SPP field across an insulating spacer without accompanying electron transport. This approach can be realized in plasmonic van der Waals heterostructures composed of strongly-biased monolayer graphene as the emitter, few-layer hexagonal boron nitride as the spacer, and silver (or gold) as the plasmonic material. In this configuration, graphene's remarkable ability to support a strongly non-equilibrium steady-state electron-hole population results in non-thermal, bias-tunable SPP emission that is uniform along the hBN/Ag interface, achieving a power conversion efficiency of up to 1% and a Purcell factor of up to 100. These findings pave the way for integrating photonic and electronic functionalities within a single two-dimensional heterostructure.