Topological Nodal Line Semimetals in CaP3 family of materials

By using first-principle calculations and k$\cdot$p model analysis, we propose that the three-dimensional (3D) topological nodal line semimetal state can be realized in CaP$_3$ family of materials, which include CaP$_3$, CaAs$_3$, SrP$_3$, SrAs$_3$ and BaAs$_3$, 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, a drumhead-like two-dimensional surface states are also obtained on the c-direction surface of these materials. When SOC is included, the nodal line will open a gap and becomes a strong topological insulator with (1;100) Z$_2$ indices.