Up to now, much of the dramatic growth in research on topological materials has focused on the topologically protected surface states. Instead, domain walls of topological materials such as Weyl semimetals provide a novel platform for the study of topological interfacial states. Such investigations have received little attention in the research community to date.

As shown in the figure, our team discovered the presence of conducting states using scanning-probe microscopy in semimetallic MoTe₂. The domain walls mark the interface between two topologically distinct phases: a topologically nontrivial Weyl semimetal T_d phase, and a "higher-order topological" 1T ' phase. Our first-principles theory elucidated the relation between the T_d and 1T ' phases in this strongly spin-orbit coupled 2D material, and explained the connection with the conducting nature of the domain walls.

The work opens new avenues to potentially useful manifestations of topology in novel materials.