Magneto tunnel conductance across twisted Weyl semimetal junctions

TL;DR

This work investigates magnetotransport across twisted Weyl semimetal junctions, revealing that interface Fermi arc states can mediate current even in the absence of a perpendicular magnetic field. A lattice model with a twist and tunable inter-slab coupling shows reconstructed interface arcs that connect same-chirality Weyl nodes, providing a zero-field transmission channel. When a magnetic field is applied, both bulk chiral Landau levels and the transverse Fermi arc channels contribute, with surface arcs dominating the conductance in mesoscopic samples at modest fields and bulk states taking over for larger samples. The findings, obtained via KWANT simulations and Landauer analysis, demonstrate a new, geometry-dependent transport mechanism and clarify its dependence on sample size, twist, and inter-slab coupling, with implications for experimental realizations of Weyl semimetal junctions.

Abstract

We investigate magnetotransport across an interface between two Weyl semimetals (finite in both directions) whose Weyl nodes project onto two different surfaces which are twisted with respect to each other before being coupled. This gives rise to a novel contribution to the conductance through the junction purely through Fermi arc states, even in the absence of a magnetic field perpendicular to the junction. When the perpendicular magnetic field is included, we find that for a mesoscopic or smaller samples, the transverse Fermi arc states have a significant contribution to the conductance for experimentally relevant fields, and need to be taken into account along with the conductance through the bulk chiral Landau levels.

Figures (10)

• Figure 1: Schematic of the transverse surface Fermi arc states living in the $x$-$z$ plane (bottom slab) and in the $y$-$z$ plane (top slab). The blue arrows signify the direction of the velocity of the transverse surface Fermi arc states on the open surfaces. The dots represent the projection of Weyl nodes on the $k_xk_y$ surface BZ, and the straight lines represent the Fermi arcs at the interface at zero tunnel coupling.
• Figure 2: Plots of the interface Fermi arcs in the interface Brillouin zone. The Fermi arcs are plotted for 6 different values of the tunnel coupling($\kappa$). For all the plots $u=0.5$. The red and blue dots are, respectively, the projections of the positive and negative chirality Weyl nodes for both the slabs on the interface BZ. It is clear from the plots that the interface Fermi arcs connect projections of the Weyl nodes of the same chirality.
• Figure 3: Figures show bulk Fermi surfaces around the Weyl nodes for chemical potential (a) $\mu=1.5$ and (b) $\mu=1.7$. The red contour belongs to the top slab and the blue contour is for the bottom slab. The bulk Fermi surfaces start to overlap and contribute in the conduction for $\mu \ge \sqrt{8/3}$.
• Figure 4: (a) The conductance is plotted for different values of $u$ and a fixed $\mu=0.5$. Figure (b) shows conductance for a fixed $u = 0.5$ and different values of the chemical potential $\mu$. We have taken $L_x = L_y = L = 45$ in the units of the lattice constant and the Weyl nodes' separation parameter $k_{0}=\pi/2$. We note that there are two peaks in the tunnel conductance and the value of the $G_{peak} \approx \frac{e^2}{h} L/2$. The peaks correspond to the values of the tunnel coupling $\kappa$ at which interface Fermi arcs almost straight.
• Figure 5: $|\langle \psi_{t+}| \psi_{b+} \rangle|$ is plotted with respect to $\kappa$. The overlap is calculated at $\mu = 0.1$, $u = 0.5$. Here $\psi_{t+}$ and $\psi_{b+}$ are the wavefunctions at momentum values close to the projections of the Weyl points of positive chirality from the top and bottom slabs respectively.