▎ 摘　　要

Band structures of armchair graphene nanoribbons (AGNRs) under crossed external fields are calculated within the tight-binding model. Magnetic field reduces energy-gap and flattens energy dispersions of band-edge states. Electric field strongly distorts energy dispersions leading to a reduction of energy-gap, a shift in band-edge states and many local maxima and minima. The complex dielectric function is further calculated in long-wavelength limit in which many peak-dip structures reveal characteristics of transparency and absorption. Furthermore, plasmon spectra are determined by frequency-position, sharpness, and number of peak-dip structures those are related to field strength and ribbon's geometry. The field-induced extra transition channels could make a change in the frequency, peak-height, and number of branch of plasmons that can make AGNRs into a tunable terahertz nano-material. The photoninduced plasmons are further reflected in the edge-structures of reflectance spectra, unveiling the transition between transparency and absorption. Reflectance spectra strongly depend on external fields and ribbon's geometry that will be verified by experimental measurements.