Electronic structure of the Si-containing topological Dirac semimetal CaA l 2 S i 2

There has been an upsurge in the discovery of topological quantum materials, where various topological insulators and semimetals have been theoretically predicted and experimentally observed. However, very few of them contain silicon, the most widely used element in the electronics industry. Recently, ternary compound $\mathrm{CaA}{\mathrm{l}}_{2}\mathrm{S}{\mathrm{i}}_{2}$ has been predicted to be a topological Dirac semimetal, hosting Lorentz-symmetry-violating quasiparticles with a strongly tilted conical band dispersion. In this work, by using high-resolution angle-resolved photoemission spectroscopy, we investigated the comprehensive electronic structure of $\mathrm{CaA}{\mathrm{l}}_{2}\mathrm{S}{\mathrm{i}}_{2}$. A pair of topological Dirac crossings is observed along the ${k}_{z}$ direction, in good agreement with the ab initio calculations, confirming the topological Dirac semimetal nature of the compound. Our study expands the topological material family on Si-containing compounds, which have great application potential in realizing low-cost, nontoxic electronic devices with topological quantum states.