Giant orbital Zeeman effects in a magnetic topological van der Waals interphase

Van der Waals (vdW) heterostructures allow the engineering of magnetic and electronic properties via interfacial orbital hybridization and charge transfer. The resulting electric fields can give rise to Rashba spin-orbit coupling and Dzyaloshinskii-Moriya interactions, which may stabilize novel two-dimensional magnetic phases. While such emergent magnetic 'interphases' may offer a promising platform for spin-based electronics, direct spectroscopic evidence for them is still lacking. Here, we report electric-field tunable Zeeman effects with Landé g-factors up to  ≈ 230 at the interface of graphene and the vdW ferromagnet Fe₃GeTe₂. They arise from an interplay of local-moment canting and the itinerant orbital moments of Fe₃GeTe₂, producing a giant asymmetric level splitting. Exploiting the inelastic phonon gap of graphene, scanning tunneling spectroscopy allows us to access the buried interface properties, and quantify Faraday-like screening. Our findings provide new insights and opportunities for electrically controlled interface magnetism, e.g. for spintronics and orbitronics devices.