Fig. 3. Symmetry analysis of edges along different directions of WTe₂.

a and b Schematic of lattice structures with edges along <100> (a) and <110> (b) directions respectively. The unit cell is shadowed in a blue rectangular in each Figure. The mirror plane M_a of the <100> direction is marked by solid line and the glide mirror plane M_b of the <010> direction is marked by dash line in Figure a, the screw axis along the <001> direction is marked by symbol 2₁. c Collection of the local photocurrent from a WTe₂ device in a Shockley-Ramo-type scheme. The solid gray lines are the weighting field lines of the device used in Fig. 2a with the source contact set at 1 V and the drain contact set at 0 V. The red arrows represent the possible directions of local edge photocurrent. The simulations are performed using COMSOL. d The distribution of Weyl nodes in bulk WTe₂ and the projections of Weyl nodes on (100), (010) and (110) surfaces. WTe₂ has eight Weyl nodes all locating in k_c = 0 plane, each four symmetry-related nodes are referred as W₁ and W₂ respectively. The mirror symmetry-related Weyl nodes with opposite chirality annihilate in pairs when projected onto (100) and (010) surfaces, but the Fermi arcs can survive in higher Miller-index surface BZs.