Topological nodal line semimetals in the CaP3 family of materials

By using first-principles calculations and a k·p model analysis, we propose that the three-dimensional topological nodal line semimetal state can be realized in the CaP3 family of materials, which includes CaP3,CaAs3,SrP3,SrAs3, and BaAs3, when spin-orbit coupling (SOC) is ignored. The closed topological nodal line near the Fermi energy is protected by time reversal symmetry and spatial inversion symmetry. Moreover, drumheadlike two-dimensional surface states are also obtained on the c-direction surface of these materials. When SOC is included, the gaps open along the nodal line and these materials become strong topological insulators with Z2 indices as (1;010).