Predicting Dirac semimetals based on Sodium Ternary Compounds

TL;DR

This paper presents a method to predict Dirac semimetals by exploring chemical compositions, successfully identifying new stable compounds with topological properties similar to known DSMs, and confirming their stability and synthesizability.

Contribution

The study introduces a chemical exploration approach to design Dirac semimetals, expanding the known family of DSMs with experimentally viable candidates.

Findings

Na2MgPb and Na2CdSn are identified as Dirac semimetals.

The candidate compounds exhibit nontrivial surface states with Fermi arcs.

All identified compounds are dynamically stable and experimentally synthesized.

Abstract

Predicting a new Dirac semimetal (DSM), as well as other topological materials, is quite challenging, since the relationship between crystal structure, composing atoms and the band topology is complex and elusive. Here, we demonstrate an approach to design DSMs via exploring the chemical degree of freedom. Based on the understanding of the well-known DSM Na$_3$Bi, three compounds in one family, namely Na$_2$MgSn, Na$_2$MgPb and Na$_2$CdSn, have been exactly located. Further hybrid-functional calculations with improved estimation of band inversion show that two of them, Na$_2$MgPb and Na$_2$CdSn, have band topology of DSMs. The nontrivial surface states with Fermi arcs on the (010) and (100) side 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 would stimulate more designs on locating topological materials based on the understanding of existing ones.