Chiral charge conservation and ballistic magnetotransport in a disordered Weyl semimetal

TL;DR

This work analyzes how topology and disorder interact in Weyl semimetals by modeling a two-node system with scalar and random-mass disorder. It shows that, despite naive expectations of inter-nodal relaxation, the chiral anomaly and average translational symmetry enforce almost exact conservation of chiral charge at the Weyl-node energy, leading to a ballistic, nondissipative magnetotransport signal in a magnetic field. A crossover length $L_a = 2 \, ext{π}^2 \, rac{oldsymbol abla oldsymbol abla}{e^3 B}$ marks the transition from diffusive to ballistic transport, with the conductance scaling as $G=rac{e^2}{h}$ per flux quantum through the cross-section in the appropriate regime. The results highlight a striking macroscopic manifestation of topology in 3D Weyl/Dirac semimetals and contrast with 2D Dirac systems, offering guidance for experimental exploration in materials such as Cr-doped Bi2Te3, where reduced disorder and Fermi-energy tuning to the nodes may enable observation of the predicted ballistic magnetotransport.

Abstract

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.