  The photovoltaic effect in a Weyl semimetal due to the adiabatic quantum
phase is studied. We particularly focus on the case in which an external ac
electric field is applied to the semimetal. In this setup, we show that a
photocurrent is induced by the ac electric field. By considering a generalized
Weyl Hamiltonian with nonlinear terms, it is shown that the photocurrent is
induced by circularly, rather than linearly, polarized light. This photovoltaic
current can be understood as an emergent electromagnetic induction in the
momentum space; the Weyl node is a magnetic monopole in the momentum space, of
which the electric field is induced by the circular motion. This result is
distinct from conventional photovoltaic effects, and potentially useful for
experimentally identifying Weyl semimetals in chiral crystals.
