Variation of topological surface states of nodal line semimetal MgB resulting from adsorption of hydrogen, hydroxide, and water molecules.

Topological semimetals have garnered significant interest due to their intrinsic topological physics and potential applications in devices. A crucial feature shared by all topological materials is the bulk-boundary correspondence, indicating the presence of unique topologically protected conducting states at the edges when non-trivial band topology exists in the bulk. Previous studies on surface states of topological materials predominantly focused on pristine surfaces, leaving the exploration of surface states in topological semimetals with adsorbates relatively uncharted.