All-Silicon Topological Semimetals with Closed Nodal Line

TL;DR

This paper predicts two stable all-silicon allotropes that are topological node-line semimetals, featuring robust nodal loops and flat surface bands, opening new avenues for silicon-based topological electronics.

Contribution

It identifies and characterizes two stable silicon allotropes as topological semimetals with protected nodal loops, expanding topological physics into silicon materials.

Findings

Two stable silicon allotropes exhibit topological nodal line semimetal behavior.

Nodal loops are protected by inversion and time-reversal symmetries.

Surface states include flat bands due to nontrivial topology.

Abstract

Owing to the natural compatibility with current semiconductor industry, silicon allotropes with diverse structural and electronic properties provide promising platforms for the next-generation Si-based devices. After screening 230 all-silicon crystals in the zeolite frameworks by first-principles calculations, we disclose two structurally stable Si allotropes (AHT-Si24 and VFI-Si36) containing open channels as topological node-line semimetals with Dirac nodal points forming a nodal loop in the kz=0 plane of Brillouin zone. Interestingly, their nodal loops protected by inversion and time-reversal symmetries are robust against SU(2) symmetry breaking due to very weak spin-orbit coupling of Si. When the nodal lines are projected onto the (001) surface, flat surface bands can be observed because of the nontrivial topology of the bulk band structures. Our discoveries extend the topological physics to the three-dimensional Si materials, highlighting the possibility to realize low-cost, nontoxic and semiconductor-compatible Si-based electronics with topological quantum states.