  The overcritical regime of axion-electrodynamics (AED) is investigated. For
magnetic fields larger than the characteristic scale linked to AED, quantum
vacuum fluctuations due to axion-like fields can dominate over those associated
with the electron-positron fields. This hypothetical regime of the dominance of
AED over QED is predicted to induce strong birefringence and screening effects.
We show that, if the magnetic field lines are curved, extraordinary photons
could be canalized along the field direction. It is also shown that the running
QED coupling depends on the magnetic field strength, and for certain energy
regimes, it could be screened almost to zero, making the QED building blocks
very weakly interacting between each other. The impact of this phenomenon on
the radiation mechanism of pulsars is discussed.
