topological semimetal candidate*

Topological semimetals are hosts of interesting types of low-energy quasiparticles such as type-I and type-II Dirac and Weyl fermions. Yet a type-III^1,2,3 emerges as a theoretical possibility exactly at the border between type-I and II, characterized by a line-like Fermi surface and a flat energy dispersion along one direction in the Brillouin Zone. A type-III fermion could undergo an electronic (Lifshitz) phase transition¹. We theoretically predict that 1T-HfTe₂ and 1T-ZrTe₂ transition metal dichalcogenides are type-I and type-II Dirac semimetals, respectively. By alloying the two materials, a new Hf_xZr_x-1Te₂ alloy with type-III Dirac cone emerges at x=0.2. We also provide experimental evidence that by using MBE, single and few layers of HfTe₂⁴, ZrTe₂⁵ and Hf_0.2Zr_0.8Te₂ can be grown on InAs(111) substrates, and by using in-situ ARPES, that the Dirac point lies at -or very close to- the E_F.

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