Observation of a three-dimensional topological Dirac semimetal phase in high-mobility Cd3As2

Symmetry-broken three-dimensional (3D) topological Dirac semimetal systems with strong spin-orbit coupling can host many exotic Hall-like phenomena and Weyl fermion quantum transport. Here, using high-resolution angle-resolved photoemission spectroscopy, we performed systematic electronic structure studies on Cd₃As₂, which has been predicted to be the parent material, from which many unusual topological phases can be derived. We observe a highly linear bulk band crossing to form a 3D dispersive Dirac cone projected at the Brillouin zone centre by studying the (001)-cleaved surface. Remarkably, an unusually high in-plane Fermi velocity up to 1.5 × 10⁶ ms^-1 is observed in our samples, where the mobility is known up to 40,000 cm² V^-1s^-1, suggesting that Cd₃As₂ can be a promising candidate as an anisotropic-hypercone (three-dimensional) high spin-orbit analogue of 3D graphene. Our discovery of the Dirac-like bulk topological semimetal phase in Cd₃As₂ opens the door for exploring higher dimensional spin-orbit Dirac physics in a real material.