▎ 摘　　要

We explore the temporal dynamics of a surface plasmon on a graphene sheet after an abrupt increase of graphene's carrier density. The plasmon is transformed into two frequency-upshifted surface plasmons propagating in the forward and backward directions, transient free-space radiation, and two-stream dc motion of carriers. The two-stream carrier motion carries zero net electric current and therefore does not generate any magnetic field. Nevertheless, it can consume a substantial fraction, up to a half, of the initial plasmon energy in the form of the kinetic energy of the carriers. We revisit the recent claim in the literature that graphene's nonstationarity can amplify plasmons.