Transport experiments in twisted (double) bilayer graphene

We study signatures in electronic transport in twisted (double) bilayer graphene. Specifically, we are interested in the coupling and decoupling between single- and bilayer graphene layers as a function of twist angle. For large twist angles, the wavefunction of the layers are decoupled. Using twisted double bilayer graphene, we determine the intrinsic energy difference between inner and outer layers of the stack. Such a crystal field opens a gap in the groundstate [1]. Since the two layers are strongly capacitively coupled but their wavefunctions can be independently tuned, the geometric capacitance between the layers is heavily affected by the finite thickness of graphene, which we determine [2]. We also show transport data at small angles, where the layers are strongly coupled. At tiny twists, we detect a topological network [3] in twisted bilayer graphene and correlated states in twisted double bilayer graphene. Finally, we study the crossover between the coupled and decoupled regime, where the wavefunctions start to spread over all layers.

[1] P. Rickhaus et al., arXiv:1910.10524 (2019)
[2] P. Rickhaus et al., arXiv:1907.00582 (2019)
[3] P. Rickhaus et al., Nano Letters ( 2018) 18 (11), 6725-6730