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Researchers show that adding a thin layer of WSe2 beside a twisted graphene moiré device can change how electrically driven magnetic switching works. By placing WSe2 next to twisted monolayer–bilayer graphene (tMBG), they use proximity-induced spin-orbit coupling (SOC) to reshape the magnetic states that underlie quantum anomalous Hall (QAH) effects. The result is a new knob to control which QAH state the device prefers when it is switched by a gate voltage.
The team made several devices where a monolayer and a bilayer of graphene are twisted together and placed on WSe2, a transition metal dichalcogenide. They measured longitudinal and Hall resistance as they varied carrier density and an electric displacement field. In devices with twist angles near 1.2–1.3°, they observed well-quantized QAH plateaus at band fillings labeled ν = 1 and ν = 3. The ν = 1 plateau appeared with an onset temperature near 3.5 K and ν = 3 near 6 K. Calculations and quantum-oscillation measurements support that WSe2 induces SOC of order meV and that the SOC strength depends on the direction of the displacement field.
At a conceptual level, spin-orbit coupling links an electron’s spin to its motion and to which valley (a momentum-space label) it occupies. In these proximitized devices the induced SOC can lock spin and valley together. That changes the magnetization of competing states and removes or shifts some magnetization reversal points—places where the preferred magnetic state flips as the gate is changed. Because the devices show strong magnetic metastability, the researchers could gate the same magnetic state between a QAH insulator and a metallic magnetic state, and between QAH states with different Chern numbers (|C| = 2 and |C| = 1) without having to reset the magnetization with a large external field.
This work matters because gate-driven, nonvolatile switching of QAH states is a promising route toward electronics that use topological edge channels. Showing that proximity-induced SOC is an effective way to engineer the magnetic energy landscape gives designers a new control parameter. In particular, the ability to tune between different topological regimes with only gate voltages could enable denser and lower-power device concepts based on chiral edge transport, once other challenges are addressed.
Important caveats remain. The QAH behavior is seen at low temperatures (a few kelvin). The devices are small and quite clean, and local defects appear to affect edge transport; the authors report sharp features they attribute to single-defect charging and note that disorder can interfere with clean edge conduction. The results come from a set of proximitized tMBG devices with WSe2 placed on the bilayer side and twist angles around 1.1–1.5°, so further work is needed to test how broadly the approach applies. The provided excerpt may also be partial and some experimental details and limits are described in the full paper.