Full Van-der-Waals Graphene/h-BN Hall Bars With Thickness-Tuned Dielectric Shielding Enable Phase-Coherent Spin Transport.

Graphene/hexagonal Boron Nitride (h-BN) devices offer high spin mobilities and atomically clean interfaces, yet spin coherence remains limited by inevitable interfacial imperfection and inseparable thickness-scattering correlations. In this work, employing a full van-der-Waals (vdW) fabrication strategy, we fabricated graphene Hall bars on 11- and 22 nm h-BN substrates, strategically selected to bracket the continuum dielectric regime where thickness-tuned screening dominates. The devices exhibit sub-ångström flatness and are devoid of interfacial bubbles, convinced by optical and scanning electron microscopy images. Magneto-transport measurements show that such clean interfaces enable phase-coherence lengths that approach the channel width, and meanwhile decouple spin transport characteristics from h-BN dielectric thickness. First-principles calculations confirm that interfacial charge transfer and proximity spin-orbit coupling saturate at the first h-BN monolayer. Additional thickness merely enhances electrostatic screening without introducing disorder. This full vdW strategy delivers a scalable, back-end-compatible materials platform for ultra-low-dissipation two-dimensional spin logic and topological superconducting circuits with atomically perfect interfaces.