Tailoring the Band Structure of Twisted Double Bilayer Graphene with Pressure

Twisted two-dimensional structures open new possibilities in band structure engineering. At magic twist angles, flat bands emerge, which gave a new drive to the field of strongly correlated physics. In twisted double bilayer graphene dual gating allows changing of the Fermi level and hence the electron density and also allows tuning of the interlayer potential, giving further control over band gaps. Here, we demonstrate that by application of hydrostatic pressure, an additional control of the band structure becomes possible due to the change of tunnel couplings between the layers. We find that the flat bands and the gaps separating them can be drastically changed by pressures up to 2 GPa, in good agreement with our theoretical simulations. Furthermore, our measurements suggest that in finite magnetic field due to pressure a topologically nontrivial band gap opens at the charge neutrality point at zero displacement field.

Automated summary

Twisted two-dimensional structures provide new possibilities for band structure engineering, with flat bands emerging at magic twist angles, driving progress in strongly correlated physics. In twisted double bilayer graphene, dual gating allows for changes in Fermi level, electron density, and interlayer potential, offering further band gap control. By applying hydrostatic pressure, additional band structure control is enabled through changes in tunnel couplings between layers, leading to significant alterations in flat bands and gaps under pressures up to 2 GPa, consistent with theoretical simulations. Moreover, measurements suggest that a topologically nontrivial band gap opens at the charge neutrality point with zero displacement field in finite magnetic field due to pressure.