Optical Properties of Graphene in External Fields

The generalized tight-binding model, with the exact diagonalization method, is developed to investigate optical properties of graphene in five kinds of external fields. The quite large Hamiltonian matrix is transferred into the band-like one by the rearrangement of many basis functions; furthermore, the spatial distributions of wave functions on distinct sublattices are utilized to largely reduce the numerical computation time. The external fields have a strong influence on the number, intensity, frequency and structure of absorption peaks, and the selection rules. The optical spectra in a uniform magnetic field exhibit plentiful symmetric absorption peaks and obey a specific selection rule. However, there are many asymmetric peaks and extra selection rules under the modulated electric field, the modulated magnetic field, the composite electric and magnetic fields, and the composite magnetic fields.