▎ 摘　　要

Transport of plasmons in graphene has been investigated by time-resolved electrical measurements. We demonstrate that the velocity v (or the refractive index proportional to v(-1)) and the characteristic impedance Z of the plasmon mode can be tuned through the carrier density. By exploiting the Z tunability, we present a gate-defined plasmonic waveguide. An important advantage of the gate-defined waveguide is dynamical switching of guiding characteristics with the gate voltages. One can tailor the patterns of gate electrodes to define two output waveguides branching off from a source waveguide, and the output waveguide can be switched by changing the gate voltages. Indeed, we show the routing in a Y-shaped channel: the path for the plasmon transmission can be selected by tuning Z of each path. These results can be well reproduced by simulation, encouraging the design of graphene-based plasmonic devices.