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The phononic and electronic properties of newly discovered quaternary superconductor ThMo₂Si₂C are reported based on the results of first-principles calculations. The phonon spectrum contains soft phonon modes around the zone corners that lead to a 221 charge-density-wave (CDW) instability, which is related to the momentum-dependent electron-phonon coupling. Intriguingly, these soft phonon modes can be removed by considering anharmonic effects. The electronic band structure without spin-orbit coupling (SOC) hosts multiple band crossing points near the Fermi level (E₅), giving rise to multiple bulk nodal lines in this system. When SOC is considered, the nodal lines are gapped out and a pair of anisotropic Dirac points protected by C₄ rotational symmetry emerge along the -Z direction near the E₅. These results suggest that superconductor ThMo₂Si₂C is a topological Dirac metal on the verge of a CDW instability, making it a realistic material platform to investigate the interplay among superconductivity, CDW quantum criticality, and bulk Dirac fermions.
Shi et al. (Tue,) studied this question.
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