  Graphene offers a possibility for actively controlling plasmon confinement
and propagation by tailoring its spatial conductivity pattern. However,
implementation of this concept has been hampered because uncontrollable plasmon
reflection is easily induced by inhomogeneous dielectric environment. In this
work, we demonstrate full electrical control of plasmon reflection/transmission
at electronic boundaries induced by a zinc-oxide-based dual gate, which is
designed to minimize the dielectric modulation. Using Fourier-transform
infrared spectroscopy, we show that the plasmon reflection can be varied
continuously with the carrier density difference between the adjacent regions.
By utilizing this functionality, we show the ability to control size, position,
and frequency of plasmon cavities. Our approach can be applied to various types
of plasmonic devices, paving the way for implementing a programmable plasmonic
circuit.
