Proximity Effect in Graphene/WSe₂ Heterojunctions Revealed by Momentum-conserved Resonant Tunneling

When monolayer graphene is brought into contact with transition metal dichalcogenide (TMD), the proximity effect is predicted to greatly enhance the spin-orbit coupling (SOC) in graphene, leading to spin splitting in the graphene's Dirac bands. In this study, we performed tunneling transport measurements in a graphene/WSe₂/graphene tunneling device, where the WSe₂ layer serves as a tunnel barrier and simultaneously enhances SOC in adjacent graphene layers. In this device, the twist angle between the two graphene layers was controlled to approximately 1° to enable momentum-conserved resonant tunneling, and the twist angle between the WSe₂ layer and each graphene layer was set to around 12° or 18° to maximize the proximity effect.

Tunneling transport measurements were performed under low temperature (1.4 K), and we observed momentum-conserved resonant tunneling between the two graphene layers. The measured peaks in the differential tunneling conductance were split into two. This can be attributed to the spin splitting of the graphene’s Dirac bands due to the proximity effect with the WSe₂ layer. From analysis of the peak positions, the SOC strength was estimated to be 8.5 meV. Notably, only two resonant peaks were observed, whereas four peaks were expected from two doubly split Dirac bands of source and drain graphene layers. This observation suggests the influence of valley-Zeeman and Rashba terms on the proximity effect, which will be discussed further in the presentation.