Abstract
Predicting new Dirac semimetals, as well as other topological materials, is challenging since the relationship between crystal structure, atoms and band topology is complex and elusive. Here, we demonstrate an approach to design Dirac semimetals via exploring chemical degree of freedom. Based on understanding of the well-known Dirac semimetal, Na3Bi, three compounds in one family, namely Na2MgSn, Na2MgPb, and Na2CdSn, are located. Furthermore, hybrid-functional calculations with improved accuracy for estimation of band inversion show that Na2MgPb and Na2CdSn have the band topology of Dirac semimetals. The nontrivial surface states with Fermi arcs on the (100) and (010) surfaces are shown to connect the projection of bulk Dirac nodes. Most importantly, the candidate compounds are dynamically stable and have been experimentally synthesized. The ideas in this work could stimulate further predictions of topological materials based on understanding of existing ones.
Highlights
Dirac semimetals (DSMs)[1–5] are the three-dimensional (3D) analogs of graphene[6] with and only with Dirac nodes on theFermi level
These Dirac nodes are formed by band crossing, and the low-energy excitation around them leads to quasiparticles described by Dirac equation as emergent massless Dirac fermions.[5,7–11]
The third one is an accidental DSM, but the band crossing points are caused by band inversion and protected by proper crystal symmetry.[2,11]
Summary
Dirac semimetals (DSMs)[1–5] are the three-dimensional (3D) analogs of graphene[6] with and only with Dirac nodes on the. The breakthrough in the search for stable DSMs11 is achieved in the series of studies on Na3Bi2,4 and Cd3As2,3,18–21 both of which were first proposed through first-principles calculations. They present good examples of the realization of the DSM in the above third class. The Dirac nodes are induced by band inversion and protected by proper axial rotational symmetry.[2,11]. Such protection makes the Dirac nodes quite robust within a finite range of Hamiltonian parameters, which is exactly the reason why this class of DSM is experimentally available while the other two remain to be found. The proposed general design principle can be used for finding new DSMs, as well as other topological materials
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