Type-III Dirac fermions in HfxZr1−xTe2 topological semimetal candidate

Abstract

Topological semimetals host interesting new types of low-energy quasiparticles such as type-I and type-II Dirac and Weyl fermions. Type-III topological semimetals can emerge exactly at the border between type-I and II, characterized by a line-like Fermi surface and a flat energy dispersion near the topological band crossing. Here, we theoretically predict that 1T-HfTe2 and 1T-ZrTe2 transition metal dichalcogenides are type-I and type-II DSMs, respectively. By alloying the two materials, a new HfxZr1−xTe2 alloy with type-III Dirac cone emerges at x = 0.2, in combination with 1% in-plane compressive strain. By imaging the electronic energy bands with in situ angle-resolved photoemission spectroscopy of this random alloy with the desired composition, grown by molecular beam epitaxy on InAs(111) substrates, we provide experimental evidence that the tοp of type-III Dirac cone lies at—or very close to—the Fermi level.