Spin-Sensitive Epitaxial In₂Se₃ Tunnel Barrier in In₂Se₃/Bi₂Se₃ Topological van der Waals Heterostructure

Current-generated spin arising from spin-momentum locking in topological insulator (TI) surface states has been shown to switch the magnetization of an adjacent ferromagnet (FM) via spin-orbit torque (SOT) with a much higher efficiency than heavy metals. However, in such FM/TI heterostructures, most of the current is shunted through the FM metal due to its lower resistance, and recent calculations have also shown that topological surface states can be significantly impacted when interfaced with an FM metal such as Ni and Co. Hence, placing an insulating layer between the TI and FM will not only prevent current shunting, therefore minimizing overall power consumption, but may also help preserve the topological surface states at the interface. Here, we report the van der Waals epitaxial growth of β-phase In₂Se₃ on Bi₂Se₃ by molecular beam epitaxy and demonstrate its spin sensitivity by the electrical detection of current-generated spin in Bi₂Se₃ surface states using a Fe/In₂Se₃ detector contact. Our density functional calculations further confirm that the linear dispersion and spin texture of the Bi₂Se₃ surface states are indeed preserved at the In₂Se₃/Bi₂Se₃ interface. This demonstration of an epitaxial crystalline spin-sensitive barrier that can be grown directly on Bi₂Se₃, and verification that it preserves the topological surface state, is electrically insulating and spin-sensitive, is an important step toward minimizing overall power consumption in SOT switching in TI/FM heterostructures in fully epitaxial topological spintronic devices.