Dirac line node (DLN) semimetals are a class of topological semimetals that feature band-crossing lines in momentum space. We study the type-I and type-II classification of DLN semimetals by developing a criterion that determines the type using band velocities. Using first-principles calculations, we also predict that Na3N under an epitaxial tensile strain realizes a type-II DLN semimetal with vanishing spin-orbit coupling (SOC), characterized by the Berry phase that is Z2-quantized in the presence of inversion and time-reversal symmetries. The surface energy spectrum is calculated to demonstrate the topological phase, and the type-II nature is demonstrated by calculating the band velocities. We also develop a tight-binding model and a low-energy effective Hamiltonian that describe the low-energy electronic structure of strained Na3N. The occurrence of a DLN in Na3N under strain is captured in the optical conductivity, which we propose as a means to experimentally confirm the type-II class of the DLN semimetal.
@article{arxiv.1807.08523,
title = {Type-II Dirac line node in strained Na3N},
author = {Dongwook Kim and Seongjin Ahn and Jong Hyun Jung and Hongki Min and Jisoon Ihm and Jung Hoon Han and Youngkuk Kim},
journal= {arXiv preprint arXiv:1807.08523},
year = {2018}
}