Electric field-controlled spin transport in a topological insulator interfaced with a ferroelectric antiferromagnet

Topological insulators have been explored extensively for spin-charge interconversion via magnetic interfaces, yet the true response of their spin-charge conversion, particularly in the absence of an external magnetic field, remains to be studied. Here, we report electric field control of spin-charge conversion in the topological insulator Bi₂Te₃ with the antiferromagnetic multiferroic BiFeO₃, using a nonlocal spin transport device. A systematic thickness dependence of the spin transport across the interface between Bi₂Te₃ and BiFeO₃ reveals a signature of topological surface-state-dominated spin transport in the bilayer system. The spin-charge conversion remains robust for thicknesses above 10 nanometers but falls rapidly with reducing thickness and vanishes at 5 nanometers. This is consistent with hybridization-induced emergence of a trivial insulating phase, which is supported by the coherency factor estimated from the magnetoconductance of Bi₂Te₃. These results establish that spin-momentum-locked surface states dominate interfacial spin transport in the decoupled regime. Beyond presenting efficient spin-charge interconversion at an entirely insulating magnetic interface, this work also highlights sputter-deposited Bi₂Te₃ as a high-quality and scalable platform for integrating quantum materials onto the devices. The nonlocal spin transport approach presented here provides a simple and unprecedented direct evidence of spin-charge conversion and opens an efficient and practical pathway toward designing energy-efficient spin-based devices.