  It has been pointed out that the axion electrodynamics exhibits instability
in the presence of a background electric field. We show that the instability
leads to a complete screening of an applied electric field above a certain
critical value and the excess energy is converted into a magnetic field. We
clarify the physical origin of the screening effect and discuss its possible
experimental realization in magnetic materials where magnetic fluctuations play
the role of the dynamical axion field.
