Based on the first-principles calculations, we reveal that TlN, a simple binary compound with wurtzite structure, is a three-dimensional (3D) topological insulator (TI) with effectively negative spin-orbit coupling ${\lambda }_{\text{eff}}<0$, which makes it distinguished from other TIs by showing opposite spin-momentum locking effect in its surface states. The sign of ${\lambda }_{\text{eff}}$ depends on the hybridization between N-$2p$ and Tl-$5d$ states, and can be tuned from negative to positive by lattice strain or chemical substitution, which drives the system into a Dirac semimetal with 3D Dirac cones in its bulk states. Such topological phase transition can be realized by electronic mechanism without breaking any crystal symmetry.

• Received 19 September 2014
• Revised 15 December 2014

DOI:https://doi.org/10.1103/PhysRevB.90.245308