Band structure and optical absorption in multilayer armchair graphene nanoribbons: A Pariser-Parr-Pople model study

摘要

Using the tight-binding and Pariser-Parr-Pople model Hamiltonians, we study the electronic structure and optical response of multilayer armchair graphene nanoribbons (AGNRs), both with and without a gate bias. In particular, the influence of the number of layers (n), and the strength of the electric field applied perpendicularly to layers, for different types of edge alignments is explored via their electro-optical properties. As a function of increasing n, the energy gap initially decreases, eventually saturating for large n. The intensity of the linear optical absorption in these systems also increases with increasing n and depends crucially on the polarization direction of the incident light and the type of the edge alignment. This provides an efficient way of determining the nature of the edge alignment, and n, in the experiments. In the presence of a gate bias, the intensity of optical absorption behaves in a nontrivial way. The absorption becomes more intense for the large fields in narrow ribbons exhibiting a redshift of the band gap with the increasing field strength, while in broad ribbons exhibiting a blueshift, the absorption becomes weaker. However, for smaller electric fields, the absorption intensity exhibits more complicated behavior with respect to the field strength. Thus, the effect of the gate bias on optical absorption intensity in multilayer AGNRs is in sharp contrast to bilayer graphene, which exhibits only enhancement of the absorption intensity with the increasing electric field.