Topological surface states induced by the magnetic proximity effect

The combination of magnetism and topological properties in one material platform is attracting significant attention due to the potential of realizing low power consumption and error-robust electronic devices. Common practice is to start from a topological material with band inversion and incorporates ferromagnetism via chemical doping or magnetic proximity effect (MPE). In this work, we show that a topological material is not necessary and that both ferromagnetism and band inversion can be established simultaneously in a trivial insulating material by MPE from a neighbouring ferromagnetic layer. This novel route is demonstrated using quantum transport measurements and first-principles calculations in a heterostructure consisting of 5-nm-thick FeO _x /1 monolayer of FeAs/3-nm-thick α-Sn. The Shubnikov–de Haas oscillations show that there is linear band dispersion with high mobility in the heterostructure even though a 3-nm-thick α-Sn single layer is a trivial semiconductor. Furthermore, first-principles calculations reveal that band inversion indeed occurs in this heterostructure, suggesting that the observed linear band is a topological surface state within this inverted gap. This work significantly expands the foundation for realizing magnetic topological materials in a myriad of trivial narrow-gap semiconductors.