Second-Order Real Nodal-Line Semimetal in Three-Dimensional Graphdiyne

Real topological phases featuring real Chern numbers and second-order boundary modes have been a focus of current research, but finding their material realization remains a challenge. Here, based on first-principles calculations and theoretical analysis, we reveal the already experimentally synthesized three-dimensional (3D) graphdiyne as the first realistic example of the recently proposed second-order real nodal-line semimetal. We show that the material hosts a pair of real nodal rings, each protected by two topological charges: a real Chern number and a 1D winding number. The two charges generate distinct topological boundary modes at distinct boundaries. The real Chern number leads to a pair of hinge Fermi arcs, whereas the winding number protects a double drumhead surface bands. We develop a low-energy model for 3D graphdiyne which captures the essential topological physics. Experimental aspects and possible topological transition to a 3D real Chern insulator phase are discussed.

Automated summary

Based on first-principles calculations and theoretical analysis, we discovered that the three-dimensional (3D) graphdiyne, which has been experimentally synthesized, is the first realistic example of the recently proposed second-order real nodal-line semimetal. The material hosts a pair of real nodal rings protected by both real Chern numbers and 1D winding numbers, resulting in distinct topological boundary modes at different boundaries. We developed a low-energy model to describe the topological physics of 3D graphdiyne and discussed experimental aspects and potential topological transition to a 3D real Chern insulator phase.