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Classification of stable three-dimensional Dirac semimetals with nontrivial topology

A three-dimensional (3D) Dirac semimetal is the 3D analog of graphene whose bulk band shows a linear dispersion relation in the 3D momentum space. Since each Dirac point with four-fold degeneracy carries a zero Chern number, a Dirac semimetal can be stable only in the presence of certain crystalline symmetries. In this work, we propose a general framework to classify stable 3D Dirac semimetals. Based on symmetry analysis, we show that various types of stable 3D Dirac semimetals exist in systems having the time-reversal, inversion, and uniaxial rotational symmetries. There are two distinct classes of stable 3D Dirac semimetals. In the first class, a pair of 3D Dirac points locate on the rotation axis, away from its center. Moreover, the 3D Dirac semimetals in this class have nontrivial topological properties characterized by 2D topological invariants, such as the $Z_{2}$ invariant or the mirror Chern number. These 2D topological indices give rise to stable 2D surface Dirac cones, which can be deformed to Fermi arcs when the surface states couple to the bulk states on the Fermi level. On the other hand, the second class of Dirac SM phases possess a 3D Dirac point at a time-reversal invariant momentum (TRIM) on the rotation axis and do not have surface states in general.