Pressure effects on bilayer graphene (BLG)/WSe₂/boron nitride (BN) device

Graphene/transition metal dichalcogenide (TMD) heterostructures combine the high mobility and gate tunability of graphene with strong spin-orbit coupling (SOC) and optical properties of 2D TMD. Clearly, in the 2D layered heterostructures, intimate contact is essential to proximity-induced phenomena such as WAL. In this study, WSe₂ is transferred to exfoliated graphene on SiO₂ by a pick-up technique and the graphene/WSe₂ heterostructure is then protected by BN on top. We apply a hydrostatic pressure up to 2 GPa to the BLG (partially covered by WSe₂)/WSe₂/BN heterostructure and observe a clear insulating behavior in the WSe₂-covered BLG region, indicating a band gap opening. This insulating behavior is enhanced as the pressure increases. However, in the uncovered BLG region, no clear insulating behavior is observed. In the meantime, we observe WAL in the WSe₂-covered region, suggesting the strongly enhanced SOC in BLG via proximity effect. The charge neutral point of BLG consistently shifts from positive to slightly negative in the covered region with increasing pressure, which is another indicator that the coupling between BLG and WSe₂ becomes stronger under high pressure.