Topological Carbon and Hourglass Dirac chain metal

Abstract:Carbon, one of the most abundant elements in universe, can take a vast number of allotropic forms. Here I introduce our recent works in revealing topological aspects in several metastable carbon allotropes. These include Weyl points, Weyl loops, and Weyl surfaces in a family of graphene networks, and triply-degenerate point and Weyl link in Pentagon Carbon. Due to the negligible spin-orbit-coupling, these objects are fundamentally distinct from those studied in strongly spin-orbit-coupled materials. If time permits, I will also discuss the Dirac chain metal. In such a material, the band-crossing-point traces out a Dirac chain — a chain of connected four-fold-degenerate Dirac loops — in the momentum space. We show that certain nonsymmorphic crystalline symmetry dictates the existence of this new phase, and we find a realistic material ReO2 for its realization.