Fig. 1: Generation of edge directional photocurrents in T_d-WTe₂ enhanced by plasmonic modes of a self-cavity.

a Top view of the crystal structure of T_d-WTe₂ with the unit cell outlined and mirror planes of the a-axis (M_a) and the glide mirror plane along the b-axis (\({\widetilde{M}}_{b}\)) marked respectively. When photoexcited (green pulse) on an edge of the flake that is not parallel to a crystal axis, a net current can form. The green arrows indicate possible current directions, whose precise direction in each device is dependent on the edge orientation^10,28. b Diagram of the cavity device geometry. The co-planar stripline on top of the heterostructure guides the emitted THz to the detector switch, and modifies the dielectric environment, which, in conjunction with the edges of the flake, defines the plasmonic self-cavity. The current density of the cavity mode (j_cavity, in blue) changes significantly underneath the metal traces, due to screening. The directional photocurrent (j_ph, indicated by the green arrow), generated at the edges, is modified by the self-cavity feedback, enhancing emission at the cavity resonance frequency.