▎ 摘　　要

It is commonly assumed that the photocurrent in two-dimensional systems with a centrosymmetric lattice is generated at structural inhomogeneities, such as p-n junctions. Here, we study an alternative mechanism of photocurrent generation associated with the inhomogeneity of the driving electromagnetic field, termed "plasmonic drag." It is associated with direct momentum transfer from the field to conduction electrons and can be characterized by a nonlocal nonlinear conductivity sigma((2))(q, omega). By constructing a classical kinetic model fully accounting for nonlocality, we show that the nonlinear conductivity is resonantly enhanced for wave phase velocity coinciding with electron Fermi velocity. The enhancement is interpreted as phase locking between electrons and the wave. We discuss a possible experiment where a nonuniform field is created by a propagating graphene plasmon and find an upper limit of the current responsivity vs plasmon velocity. This limit is set by a competition between resonantly growing a sigma((2))(q, omega) and the diverging kinetic energy of electrons as the wave velocity approaches the Fermi velocity.