▎ 摘　　要

Based on the density matrix description of carriers in bilayer graphene, the effect of an oscillating perpendicular electric field is considered. When the frequency of the applied field matches the internal eigen-frequency, a sharp step appears in the imaginary part of the electric susceptibility. This peculiarity is due to the unusual interconnection between electron and hole states in graphene. (C) 2009 Elsevier B.V. All rights reserved.