▎ 摘　　要

We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on cesium (Cs) intercalated bilayer graphene with a Cs overlayer (Cs-C8CsC8). Low-energy electron diffraction shows a (2 x 2) pattern consistent with intercalation of a Cs layer similar to bulk C8Cs, in addition to the signature of a nearly commensurate superstructure created by the Cs overlayer. ARPES results reveal folding of the pi bands due to the periodic (2 x 2) potential of the intercalated Cs atoms, together with a free-electron-like state at the Gamma point. Significant mass renormalization is observed in the band dispersion near the Fermi level, indicative of strong electron-phonon coupling. Based on analysis of the self-energy, we find anisotropic electron-phonon coupling with an estimated strength of lambda = 0.38 +/- 0.02 in the K-Gamma direction, and lambda = 0.60 +/- 0.02 in the K-M direction. This coupling is much larger than that of other doped graphenes, and comparable to superconducting bulk GICs. We attribute this large electron-phonon coupling constant to the presence of the Cs overlayer, which highly dopes pi* bands, and creates a structure similar to stage-I graphite intercalation compounds.