A stable three-dimensional topological Dirac semimetal Cd3As2

A state of matter known as a three-dimensional Dirac semimetal has latterly garnered significant theoretical and experimental attention. Using angle-resolved photoelectron spectroscopy, it is shown that Cd 3 As 2 is an experimental realization of a three-dimensional Dirac semimetal that is stable at ambient conditions. Three-dimensional (3D) topological Dirac semimetals (TDSs) are a recently proposed state of quantum matter 1 , 2 , 3 , 4 , 5 , 6 that have attracted increasing attention in physics and materials science. A 3D TDS is not only a bulk analogue of graphene; it also exhibits non-trivial topology in its electronic structure that shares similarities with topological insulators. Moreover, a TDS can potentially be driven into other exotic phases (such as Weyl semimetals 1 , 7 , axion insulators 1 , 4 and topological superconductors 8 , 9 ), making it a unique parent compound for the study of these states and the phase transitions between them. Here, by performing angle-resolved photoemission spectroscopy, we directly observe a pair of 3D Dirac fermions in Cd 3 As 2 , proving that it is a model 3D TDS. Compared with other 3D TDSs, for example, β-cristobalite BiO 2 (ref. 3 ) and Na 3 Bi (refs 4 , 5 ), Cd 3 As 2 is stable and has much higher Fermi velocities. Furthermore, by in situ doping we have been able to tune its Fermi energy, making it a flexible platform for exploring exotic physical phenomena.