Superconducting topological Dirac semimetals: P6/m−Si6 and P6/m−NaSi6

Abstract

We theoretically propose that hexagonal silicon-based crystals P6/m−Si6 and P6/m−NaSi6 are topological Dirac semimetals with superconducting critical temperatures of 12 K and 13 K, respectively, at ambient pressure. Band inversion occurs with the Fu-Kane topological invariant Z2=1, even in the absence of spin-orbit coupling. The Dirac nodes protected by C6 crystal rotational symmetry remain gapless with spin-orbit coupling. Using first-principles calculations, we find pressure-induced topological phase transitions for P6/m−Si6 and P6/m−NaSi6 with critical external pressures of 11.5 GPa and 14.9 GPa, respectively. Above the critical pressures, the Dirac bands are gapped with Z2=0, while the superconducting states and the crystal symmetries are retained. Our results may shed light into a search for silicon-based topological materials with superconductivity.

Source-reported materials — not catalogue approval

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