Chiral charge conservation and ballistic magnetotransport in a disordered Weyl semimetal

We demonstrate that in an ideal Weyl semimetal, in which the Fermi energy coincides with the band-touching nodes, weak direct inter-nodal scattering is irrelevant and, as a result, the chiral charge is (almost) exactly conserved. This leads to an experimentally-observable effect: in an applied magnetic field, the charge transport along the field becomes purely ballistic, with the conductance given by $e^2/h$ per magnetic flux quantum through the sample cross-section. This is the strongest experimental manifestation of nontrivial topology in Weyl and Dirac semimetals.