  The low-energy quasiparticles of Weyl semimetals are a condensed-matter
realization of the Weyl fermions introduced in relativistic field theory.
Chiral anomaly, the nonconservation of the chiral charge under parallel
electric and magnetic fields, is arguably the most important phenomenon of Weyl
semimetals and has been explained as an imbalance between the occupancies of
the gapless, zeroth Landau levels with opposite chiralities. This widely
accepted picture has served as the basis for subsequent studies. Here we report
the breakdown of the chiral anomaly in Weyl semimetals in a strong magnetic
field based on ab initio calculations. A sizable energy gap that depends
sensitively on the direction of the magnetic field may open up due to the
mixing of the zeroth Landau levels associated with the opposite-chirality Weyl
points that are away from each other in the Brillouin zone. Our study provides
a theoretical framework for understanding a wide range of phenomena closely
related to the chiral anomaly in topological semimetals, such as
magnetotransport, thermoelectric responses, and plasmons, to name a few.
