High-fidelity electrical detection of spin transport in graphene.

Graphene can support spin transport over long distances, yet achieving large electrical spin signals remains challenging because spin injection and detection are highly sensitive to disorder at tunnel-barrier interfaces. Here we demonstrate that suppressing such interfacial disorder enables high-fidelity spin injection and detection in graphene. We fabricate van der Waals graphene spin valves by exfoliating and assembling constituent two-dimensional crystals inside an inert glovebox, combined with contamination-suppressing lamination and thorough post-transfer cleaning to realize atomically flat hexagonal boron nitride tunnel barriers. Our four-terminal nonlocal devices exhibit exceptionally large spin polarizations approaching 90 percent and nonlocal spin signals up to 1.6 kΩ. The high tunnel-barrier quality enables robust spin detection down to nanoampere excitation currents and gate-tunable magnetoresistance exceeding 80 percent. Spin precession measurements reveal Elliott-Yafet-type relaxation with nearly isotropic spin dynamics. These results establish interface-controlled van der Waals fabrication as an effective route to high-signal spin transport in graphene.