Realization of a two-dimensional Weyl semimetal and topological Fermi strings

The development of two-dimensional (2D) Weyl semimetals, akin to graphene but with spinful characteristics, marks a significant advancement in topological materials. These materials exhibit complex spin-polarized linear band structures, enabling unique topological phenomena such as Fermi string edge states. Our experimental work introduces alpha-bismuthene, a monolayer 2D Weyl semimetal synthesized via molecular beam epitaxy (MBE). Utilizing techniques like spin- and angle-resolved photoemission spectroscopy (ARPES) we confirmed the presence of spin-polarized Weyl cones and Weyl nodes. Our report on alpha-bismuthene also includes findings from scanning tunneling spectroscopy (STS), which experimentally confirmed the presence of Fermi strings, a topological edge state. These findings not only verify the topological properties of the material but also enhance the exploration of Weyl fermions in reduced dimensions, pushing the boundaries of topological quantum materials research.