Dirac Line Nodes in Inversion Symmetric Crystals

TL;DR

This paper introduces a new class of topological semimetals characterized by Dirac Line Nodes in inversion symmetric crystals, predicted through first-principles calculations, with potential for experimental realization and unique surface states.

Contribution

It proposes a $ ext{Z}_2$ topological classification for Dirac Line Nodes in inversion symmetric semimetals without spin--orbit coupling, supported by first-principles predictions in Cu$_3$N.

Findings

DLNs predicted in Cu$_3$N via doping with Zn and Pd

Presence of nearly-flat surface states associated with DLNs

Parity eigenvalues used to determine topological invariants

Abstract

We propose and characterize a new $\mathbb{Z}_2$ class of topological semimetals with a vanishing spin--orbit interaction. The proposed topological semimetals are characterized by the presence of bulk one-dimensional (1D) Dirac Line Nodes (DLNs) and two-dimensional (2D) nearly-flat surface states, protected by inversion and time--reversal symmetries. We develop the $\mathbb{Z}_2$ invariants dictating the presence of DLNs based on parity eigenvalues at the parity--invariant points in reciprocal space. Moreover, using first-principles calculations, we predict DLNs to occur in Cu$_3$N near the Fermi energy by doping non-magnetic transition metal atoms, such as Zn and Pd, with the 2D surface states emerging in the projected interior of the DLNs. This paper includes a brief discussion of the effects of spin--orbit interactions and symmetry-breaking as well as comments on experimental implications.