LAUSR

Three-dimensional topological Dirac semimetals are a new state of matter. The authors report on experiments that directly access the electronic structure of two-dimensional states in the prototype topological Dirac semimetal Cd${}_{3}$As${}_{2}$. By modulating the carrier density of very thin, epitaxial Cd${}_{3}$As${}_{2}$ films, using the electric field effect, the authors tune the electronic states through a two-dimensional Dirac point, as evidenced by a minimum in the density of states. Moreover, the linear energy dispersion and the presence of a zero-energy Landau level establish the topological nature of the two-dimensional states in this three-dimensional Dirac semimetal.