Intrinsic Magnetic Topological Insulator State Induced by the Jahn-Teller Effect

The Jahn-Teller effect is a geometrical distortion which lowers the system symmetry and lifts orbital degeneracy in molecules and solids. It affects a wide range of properties, including magnetic and band structures. In this work we propose a family of Cr-containing intrinsic magnetic topological insulator materials which are subjected to a pseudo-Jahn-Teller effect-CrBi₂Se₄, CrBi₂Te₂Se₂, and CrBi₂Te₄. Using first-principles calculations we study their properties and investigate the impact of Jahn-Teller distortions on the electronic and magnetic properties. We show that these distortions can significantly affect magnetic anisotropy energy and band structure. Without the distortions accounted for, all three of the compounds exhibit a semimetallic band structure. The distortions open a band gap, which in the cases of CrBi₂Te₂Se₂ and CrBi₂Te₄ is inverted. We also investigate the CrBi₂Te₂Se₂ and CrBi₂Te₄ surface band structure and demonstrate that the surface states have a topological origin.