Magnetic breakdown and chiral magnetic effect at Weyl-semimetal tunnel junctions

We investigate magnetotransport across an interface between two Weyl semimetals whose Weyl nodes project onto different interface momenta. Such an interface generically hosts Fermi arcs that connect Weyl nodes of identical chirality in different Weyl semimetals (homochiral connectivity)—in contrast to surface Fermi arcs that connect opposite-chirality Weyl nodes within the same Weyl semimetal (heterochiral connectivity). We show that electron transport along homochiral-connectivity Fermi arcs, in the presence of a longitudinal magnetic field, results in a universal longitudinal magnetoconductance of $e^2/h$ per magnetic flux quantum. Furthermore, a weak tunnel coupling can result in a close encounter of two homochiral-connectivity Fermi arcs, enabling magnetic breakdown. Above the breakdown field the interface Fermi arc connectivity is effectively heterochiral, leading to a saturation of the conductance.

Figure 1

Spectral flow at the interface between two Weyl semimetals with a longitudinal magnetic field. (a) Interface Fermi arcs with homochiral connectivity (orange lines) lead to a full transmission of the chiral zeroth Landau level across the interface (indicated by thick red/blue arrows going from/to the Landau-level spectrum) while the higher Landau levels are reflected. (b) Same as (a) but for heterochiral connectivity of Fermi arcs (green lines), in which case the chiral Landau levels are reflected.

Figure 2

(a) The interface of two WSMs with crossing Fermi arcs whose hybridization leads to a connectivity switch from heterochiral to homochiral. (b) The close encounter of interface Fermi arcs for a weak tunnel coupling.

Figure 3

Conductance, in units of the saturation value $(e^2/h)N\left(B_0\right)$, as a function of the magnetic field in units of the breakdown field $B_0$. The numerical computation is performed for model parameters $b=\pi /2$, energy $E=0.1$, and various values of $\theta$ and $\kappa$. The analytical result (black dashed curve) are in good agreement with the numerical results, with increasing deviations close to the field's upper bound (see below). The straight dashed lines indicate the predicted asymptotic low- and high-field behavior. For the numerical data, the upper bound on the magnetic field is set by the smallest magnetic length ${\ell }_B=3.1$ lattice units—since smaller ${\ell }_B$ results in a trivial breakdown of WSM physics—while the lower bound is set to 13.8 lattice units. Data points corresponding to a smaller (larger) breakdown field $B_0$ [for smaller (larger) $\kappa$] thus span a range of fields at higher (lower) values of $B/B_0$. The inset shows a close-up at small fields; highlighting the deviation from perfect transmission caused by the onset of magnetic breakdown.