Epitaxial In₂Se₃ as a spin sensitive barrier for electrical detection of current generated spin in the topological insulator Bi₂Se₃

Amorphous tunnel barriers such as aluminum oxide have typically been utilized to detect spin polarizations generated by spin-momentum locking in topological insulators (TIs) such as Bi₂Se₃.  Here we report epitaxial crystalline In₂Se₃ grown by molecular beam epitaxy as a spin sensitive barrier on Bi₂Se₃, where both share a similar structure and a common anion.  Raman spectroscopy indicate that the In₂Se₃ is β-phase.  Density function theory (DFT) calculations confirm that the linearly dispersing Bi₂Se₃ surface states and their spin-momentum locking is preserved at the Bi₂Se₃/β-In₂Se₃ interface. Spin potentiometric measurements on epitaxial Fe/In₂Se₃/Bi₂Se₃ heterostructures demonstrated electrical detection of the current-generated spin in the topologically protected Bi₂Se₃ surface states arising from spin-momentum locking, where the projection of the TI spin onto the magnetization of the ferromagnet is manifested as a voltage.  Distinct low and high voltage signals are measured depending on the parallel or antiparallel alignment of TI spin and magnetization.  These results demonstrate that In₂Se₃ is a viable spin sensitive barrier for the detection of current-generated spins in TI. This first demonstration of an epitaxial crystalline spin sensitive barrier that can be grown directly on Bi₂Se₃ is an important step towards fully epitaxial topological spintronic devices.