Confinement induced topological phase transition in thin film rare-earth pnictides

The metal-insulator phase transition is a classical phenomenon induced by various effects. The transition caused by size-quantization in going from a bulk material to the very thin film limit is well-known. By using first principles simulation methods, we investigate the phase transition when a 3D bulk semimetallic rare-earth pnictide becomes as thin as the 2D material. Due to the unique electronic structure of the rare-earth pnictides, different electron pockets in the Brillouin zone of the material shift differently upon the size-quantization with certain pockets shifting only weakly due to confinement to 2D. This small shift prevents a trivial gap opening in thin film rare-earth pnictides that are thin in one direction. More interestingly, there is eventually a topological phase transition from a semimetal to a 2D spin Hall insulator/Chern insulator with a sizeable 2D bulk gap due to spin-orbit coupling interaction. This finding introduces a new member to the 2D spin Hall insulator/Chern insulator family and offers a new platform to realize the 2D spin Hall insulator/Chern insulator experimentally.