Signature of the chiral anomaly in ballistic Weyl junctions

Abstract

Massless relativistic particles possess an extra quantum number: their chirality. However this chirality ceases to be a conserved quantity in the presence of colinear electric and magnetic fields, which is a manifestation of the chiral anomaly. Weyl materials possess low energy electrons whose dynamics mimics that of massless relativistic particles. Here we show that ballistic transport through such a material is the appropriate regime to unveil this chiral anomaly. We compute the magnetoconductance of a short junction made out of such a Weyl semi-metal. We show that it displays quantum oscillations at low magnetic field and low temperature, before reaching a universal high-field regime where it increases linearly with the field. At low fields, the algebraic-in-field magnetoconductance results from the interplay between both chiral and non-chiral conducting channels. By contrast, the linear conductance at higher fields, with a universal proportionality factor e3/h2 per unit area of the conductor's cross-section, constitutes an unambiguous signature of the chiral anomaly in a Weyl conductor. Finally, we study the dependence of the ballistic magneto-conductance on the chemical potential, and discuss the cross-over towards the diffusive regime when elastic scattering is present.