Surface plasmon enhancement of spontaneous emission in graphene waveguides

This work analyzes the spontaneous emission of a single emitter placed near the graphene waveguide formed by two parallel graphene monolayers, with an insulator spacer layer. In this case, the eigenmodes supported by the structure, such as surface plasmon and wave guided modes, provide decay channels for the electric dipole placed close to the waveguide. We calculated the contribution to the decay rate of symmetric and antisymmetric eigenmodes as a function of frequency and the orientation of the emitter. Our results show that the modification of the spontaneous emission due to excitation of guided modes is much lower than the corresponding decays through the excitation of symmetric and antisymmetric surface plasmons, for which, the spontaneous emission is dramatically enhanced. As a consequence of the high confinement of surface plasmons in the graphene waveguide, we found that the decay rate of the emitter with vertical orientation (with respect to graphene sheets) is twice the corresponding decay of the same emitter with parallel orientation in the whole frequency range where surface plasmon modes exist. Differently from metallo- dielectric structures, where structural parameters determine the range and magnitude of this emission, our work shows that, by dynamically tuning the chemical potential of graphene, the spectral region where the decay rate is enhanced can be chosen over a wide range.