Electronic Collective Mode Behaviors in Doped and Gated Armchair-Type Graphene Nanoribbons

Motivated by the recent nanophotonic community, in this work, we address the behavior of quantized charge-density fluctuations of doped and gated semiconductor armchair-type graphene nanoribbons within the tight-binding model and the Green’s function technique. In particular, we study the behavior of frequency-dependent susceptibility, when the system is exposed to photons or electrons. Injecting electrons by doping or ejecting ones by gating lead to different treatments in response function. Doping offers new collective modes due to added states between the valence and conduction bands (provided by the density of states) corresponding to intraband transitions, while gating distributes intraband modes. The results show that both ribbon width and doping concentrations affect the intraband transitions in electro-optical devices. Another remarkable point is the strong sensitivity of intraband plasmons to the direction of incoming photons or electrons. We found that the susceptibility of doped nanoribbons vanishes at perpendicular angles due to the distribution of intraband modes.