Guided Plasmons in Graphene $p\mathrm{\text{−}}n$ Junctions

Spatial separation of electrons and holes in graphene gives rise to the existence of plasmon waves confined to the boundary region. A theory of such guided plasmon modes within hydrodynamics of electron-hole liquid is developed. For plasmon wavelengths smaller than the size of charged domains, plasmon dispersion is found to be $\omega \propto q^{1/4}$. The frequency, velocity, and direction of propagation of guided plasmon modes can be easily controlled by the external electric field. In the presence of a magnetic field, a spectrum of additional gapless magnetoplasmon excitations is obtained. Our findings indicate that graphene is a promising material for nanoplasmonics.

Figure 1

Two types of graphene $p\mathrm{\text{−}}n$ junctions: (a) field-induced, (b) gate-induced. Dot-dashed line indicates boundary between electron and hole regions and, correspondingly, the direction of plasmon propagation. In case of field-induced junction, it is controlled by the direction of external electric field $E_0$.