Electrostatically Tunable and Topological-Edge-States-Associated Spin-Charge Conversion in Bilayer WTe2.

Topological edge/surface states, characterized by spin-momentum locking and topological protection, can provide efficient channels for spin-charge conversion and are valuable for low-power spintronics. Electrostatic tunability, on the other hand, is crucial in both fundamental studies and practical applications of spintronic devices. However, typical topological edge states are gapless and thus the associated spin-charge conversion is generally insensitive to electrostatic gating. Here, we report electrostatically tunable spin-charge conversion in bilayer WTe2, with behavior most consistently explained by a substantial contribution from residual topological edge states. Compared with thicker semimetallic WTe2 reference devices, the bilayer WTe2 exhibits an order-of-magnitude enhancement in conversion efficiency, which can be significantly modulated with gate voltages. Theoretical calculations reveal that, after interlayer hybridization, residual topological edge states with a small energy gap persist in bilayer WTe2 and retain spin-momentum-locked character. The calculated edge-state-related spin Hall conductance is strongly Fermi-level dependent and becomes enhanced near the charge-neutrality regime, consistent with the experimentally observed gate-dependent spin-charge conversion. These results suggest that partially preserved topological edge states can substantially contribute to both enhancement and electrostatic tunability of spin-charge conversion in bilayer WTe2, providing a potential route toward gate-reconfigurable van der Waals spintronic devices.