I4/mcm-Si₄₈: An Ideal Topological Nodal-Line Semimetal

Topological semimetals (TSMs) have attracted much attention due to their exotic physical properties and great application potential. Silicon-based TSMs are of particularly importance because of their abundance, nontoxicity, and natural compatibility with the current semiconductor industry. In this work, an ideal low-energy topological nodal-line semimetal (TNLSM) silicon (I4/mcm-Si₄₈) with a clean band crossing at the Fermi level is screened from thousands of silicon allotropes by general and transferable tight-binding and DFT calculations. The results of formation energy, phonon dispersion, ab initio molecular dynamics, and elastic constants show that I4/mcm-Si₄₈ possesses good stability and is more stable than several synthesized silicon structures. Furthermore, I4/mcm-Si₄₈ exhibits exotic photoelectric properties, and the Dirac fermions with high Fermi velocity (3.4–4.36 × 10⁵ m/s) can be excited by low-energy photons. Our study provides a promising topological nodal-line semimetal for fundamental research and potential applications in semiconductor-compatible high-speed photoelectric devices.