Twisted two-dimensional structures open new possibilities in band structure engineering. In twisted graphene heterostructures, the small relative rotation of two graphene layers changes their band structure drastically. In twisted bilayer graphene at magic twist angles, flat bands emerge, which give a new drive to the field of strongly correlated physics [1]. The twisted double bilayer graphene is also an interesting system with correlated and topologically non-trivial phases. In this system the dual gating allows changing of the Fermi level, hence the electron density, and allows tuning the interlayer potential, giving further control over band gaps [2,3,4]. In this talk, I show that by applying hydrostatic pressure, additional control of the band structure becomes possible due to the tunability of tunnel couplings between the layers [5]. The band structure can be drastically changed by pressure, in good agreement with our simulations. Furthermore, our measurements suggest that the pressure can decrease the correlation effects.

 

[1] Cao, Y.; Fatemi, V.; Fang, S.; Watanabe, K.; Taniguchi, T.; Kaxiras, E.; Jarillo-Herrero, P. Unconventional superconductivity in magic-angle graphene superlattices. Nature 2018, 556, 43-50.

 

[2] Cao, Y.; Rodan-Legrain, D.; Rubies-Bigorda, O.; Park, J. M.; Watanabe, K.; Taniguchi, T.; Jarillo-Herrero, P. Tunable correlated states and spin-polarized phases in twisted bilayer-bilayer graphene. Nature 2020, 583, 215-220.

 

[3] He, M.; Li, Y.; Cai, J.; Liu, Y.; Watanabe, K.; Taniguchi, T.; Xu, X.; Yankowitz, M. Symmetry breaking in twisted double bilayer graphene. Nature Physics 2020, 17, 26-30.

 

[4] Liu, X.; Hao, Z.; Khalaf, E.; Lee, J. Y.; Ronen, Y.; Yoo, H.; Najafabadi, D. H.; Watanabe, K.; Taniguchi, T.; Vishwanath, A.; Kim, P. Tunable spin-polarized correlated states in twisted double bilayer graphene. Nature 2020, 583, 221-225.

 

[5] Szentpéteri, B.; Rickhaus, P.; de Vries, F. K.; Márffy, A.; Fülöp, B.; Tóvári, E.; Watanabe, K.; Taniguchi, T.; Kormányos, A.; Csonka, Sz.; Makk, P. Tailoring the band structure of twisted double bilayer graphene with pressure. Nano Letters 2021.