Heterostructures can be assembled from atomically thin materials by combining a wide range of available van der Waals crystals, providing exciting possibilities for designer electronics1. In many cases, beyond simply realizing new material combinations, interlayer interactions lead to emergent electronic properties that are fundamentally distinct from those of the constituent layers2. A critical parameter in these structures is the interlayer coupling strength, but this is often not easy to determine and is typically considered to be a fixed property of the system. Here we demonstrate that we can controllably tune the interlayer separation in van der Waals heterostructures using hydrostatic pressure, providing a dynamic way to modify their electronic properties. In devices in which graphene is encapsulated in boron nitride and aligned with one of the encapsulating layers, we observe that increasing pressure produces a superlinear increase in the moiré-superlattice-induced bandgap—nearly doubling within the studied range—together with an increase in the capacitive gate coupling to the active channel by as much as 25 per cent. Comparison to theoretical modelling highlights the role of atomic-scale structural deformations and how this can be altered with pressure. Our results demonstrate that combining hydrostatic pressure with controlled rotational order provides opportunities for dynamic band-structure engineering in van der Waals heterostructures.
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We thank P. San-Jose, J. Song, A. Shytov, L. Levitov, J. Wallbank and P. Moon for theoretical discussions. This work was supported by the National Science Foundation (NSF) (DMR-1462383). C.R.D. acknowledges partial support from the David and Lucille Packard foundation. Development of the device concept and fabrication process was partially supported by the NSF MRSEC program through Columbia in the Center for Precision Assembly of Superstratic and Superatomic Solids (DMR-1420634). We acknowledge S. Tozer for use of his 16 T PPMS which is partially supported as part of the Center for Actinide Science and Technology (CAST), an Energy Frontier Research Center (EFRC) funded by the Department of Energy, Office of Science, Basic Energy Sciences under award no. DE-SC0016568. A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by NSF Cooperative Agreement no. DMR-1157490, the State of Florida and the US Department of Energy and additionally provided support for pressure cell development through User Collaboration Grant Program (UCGP) funding. J.J. and N.L. were supported by the Korean NRF through grant NRF-2016R1A2B4010105 and Korean Research Fellowship grant NRF-2016H1D3A1023826, and B.L.C. was supported by grant NRF-2017R1D1A1B03035932. E.L. and S.A. are supported by the National Research Foundation of Singapore under its Fellowship program (NRF-NRFF2012-01) and the Singapore Ministry of Education AcRF Tier 2 (MOE2017-T2-2-140). K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, and JSPS KAKENHI grant no. JP15K21722.