▎ 摘　　要

Josephson effect in a planar graphene junction is studied by assuming that the coupling of a graphene sheet and two superconductors deposited on its top is described by a tunneling Hamiltonian. This model properly takes account of the proximity effect characteristic to a planar junction, and allows us to treat monolayer and bilayer cases in a parallel manner. Applying a quasiclassical Green's function approach to it we analyze the Josephson critical current I-c in a short-junction limit. As a characteristic feature of the planar junction we find that I-c is a concave function of temperature at the strong coupling limit while it crosses over to a convex function with decreasing the coupling strength. We also find different chemical-potential dependences of I-c in the monolayer and bilayer cases.