A first principle study of interband transitions and electron energy loss in mono and bilayer graphene: Effect of external electric field

We present comparative electronic and dielectric response of mono and bilayer graphene using the first principle pseudopotential and localized basis set based approach. It is found that interband transitions show negligible change in bilayer graphene with respect to the monolayer graphene except π→σ⁎ transitions for which 1.7 eV blue shift have been found. EEL spectra show variable blue shift ranging between 0.1 eV and 7.9 eV for bilayer graphene with respect to the monolayer graphene for both in-plane and out-of-plane polarization. Electronic band structure and dielectric response in the infrared region up to 1 eV of bilayer graphene on the application of externally applied electric field between 0.5 V/nm to 3.0 V/nm have also been investigated. We have obtained the induced band gap that is in good agreement with the experiment [4] when the applied electric field is less than 2.0 V/nm. Plasmonic excitations have been found to vanish on increasing the intensity of external electric field. Structures in imaginary part of dielectric function (ϵ2) at different electric fields are found to be consistent with the induced band gap and are most likely due to excitonic transition.