Prediction of TiRhAs as a Dirac Nodal Line Semimetal via First-Principles Calculations

Using first-principles calculations, we predict that TiRhAs, a previously synthesized compound, is a Dirac nodal line (DNL) semimetal. The DNL in this compound is found to be protected both by the combination of inversion and time-reversal symmetry, and by a reflection symmetry, in the absence of spin-orbit coupling (SOC). Our calculations show that band velocities associated with the nodal line have a high degree of directional anisotropy, with in-plane velocities v⊥ perpendicular to the nodal line between 1.2–2.8×105 m/s. The crossings along the DNL are further found to exhibit a prominent and position-dependent tilt along directions perpendicular to the nodal line. We calculate Z2 indices based on parity eigenvalues at time-reversal invariant momenta and show that TiRhAs is topological. A tight-binding model fit from our first-principles calculations demonstrates the existence of two-dimensional drumhead surface states on the surface Brillouin zone. Based on the small gapping of the DNL upon inclusion of SOC and the clean Fermi surface free from trivial bands, TiRhAs is a promising candidate for further studies of the properties of topological semimetals.