Observation of Topological Edge States at the Step Edges on the Surface of Type-II Weyl Semimetal TaIrTe₄

Topological materials harbor topologically protected boundary states. Recently, TaIrTe₄, a ternary transition-metal dichalcogenide, was identified as a type-II Weyl semimetal with the minimal nonzero number of Weyl points allowed for a time-reversal invariant Weyl semimetal. Monolayer TaIrTe₄ was proposed to host topological edge states, which, however, lacks of experimental evidence. Here, we report on the topological edge states localized at the monolayer step edges of the type-II Weyl semimetal TaIrTe₄ using scanning tunneling microscopy. One-dimensional electronic states that show substantial robustness against the edge irregularity are observed at the step edges. Theoretical calculations substantiate the topologically nontrivial nature of the edge states and their robustness against the edge termination and layer stacking. The observation of topological edge states at the step edges of TaIrTe₄ surfaces suggests that monolayer TaIrTe₄ is a two-dimensional topological insulator, providing TaIrTe₄ as a promising material for topological physics and devices.