Nanostructured Carbon Allotropes with Weyl-like Loops and Points

TLDR

Carbon allotropes are intensely studied for their structural, electronic, and chemical properties, yet their topological band characteristics have been overlooked due to weak spin–orbit coupling. The authors demonstrate that conjugated p‑orbital interactions in carbon can generate a Weyl‑like semimetal without spin–orbit coupling. Using first‑principles calculations and tight‑binding models on a stable interpenetrated graphene network, they show that its Fermi surface contains symmetry‑protected Weyl‑like loops that collapse into points when inversion symmetry is broken. These topological features produce a surface flat band for the loop case and two Fermi arcs for the point case, and the materials may also serve as catalysts.

Abstract

Carbon allotropes are subject of intense investigations for their superb structural, electronic, and chemical properties, but not for topological band properties because of the lack of strong spin–orbit coupling (SOC). Here, we show that conjugated p-orbital interactions, common to most carbon allotropes, can in principle produce a new type of topological band structure, forming the so-called Weyl-like semimetal in the absence of SOC. Taking a structurally stable interpenetrated graphene network (IGN) as example, we show, by first-principles calculations and tight-binding modeling, that its Fermi surface is made of two symmetry-protected Weyl-like loops with linear dispersion along perpendicular directions. These loops are reduced to Weyl-like points upon breaking of the inversion symmetry. Because of the topological properties of these band-structure anomalies, remarkably, at a surface terminated by vacuum there emerges a flat band in the loop case and two Fermi arcs in the point case. These topological carbon materials may also find applications in the fields of catalysts.