Three-dimensional Dirac semimetal and quantum transport in Cd 3 As 2

Based on the first-principles calculations, we recover the silent topological nature of Cd${}_{3}$As${}_{2}$, a well known semiconductor with high carrier mobility. We find that it is a symmetry-protected topological semimetal with a single pair of three-dimensional (3D) Dirac points in the bulk and nontrivial Fermi arcs on the surfaces. It can be driven into a topological insulator and a Weyl semimetal state by symmetry breaking, or into a quantum spin Hall insulator with a gap more than 100 meV by reducing dimensionality. We propose that the 3D Dirac cones in the bulk of Cd${}_{3}$As${}_{2}$ can support sizable linear quantum magnetoresistance even up to room temperature.