Van Hove singularity, flat band, and phonon-mediated superconductivity in topological perovskite carbides

Recently, the emergence of van Hove singularity, flat band, and Dirac cone in kagome materials has attracted tremendous interest as they are closely related to the superconductivity. Here, based on first-principles calculations, we propose these features can be realized in the topological pervoskites $A{\mathrm{CPd}}_{3}$ $(A=\text{Mg}, \mathrm{Ca}, \mathrm{Sr})$. In particular, the Dirac point is observed near the Fermi level with the spin-orbit coupling. The superconducting transition temperature ${T}_{c}$ is estimated to be 19.05, 15.37, and 10.25 K for ${\mathrm{MgCPd}}_{3}$, ${\mathrm{CaCPd}}_{3}$, and ${\mathrm{SrCPd}}_{3}$ by solving the Allen-Dynes modified McMillan formula, respectively. In general, the high ${T}_{c}$ can be attributed to the large electronic density of states near the Fermi level, which arises from the van Hove singularity and flat band. Noticeably, the declining trend of ${T}_{c}$ from ${\mathrm{MgCPd}}_{3}$ to ${\mathrm{SrCPd}}_{3}$ can be ascribed to the decreasing electron-phonon coupling that is related to the weakening of electron correlation. This point is further verified by doping holes (electrons) in ${\mathrm{CaCPd}}_{3}$, i.e., the ${T}_{c}$ would gradually increase to 18.41 K when the flat band gets more and more dispersionless. Thus these pervoskites provide solid platforms to explore the interplay among band topology, electron correlation and superconductivity.