Fabry-Perot cavities and quantum dot formation at gate-defined interfaces in twisted double bilayer graphene

The rich and electrostatically tunable phase diagram exhibited by moire materials has made them a suitable platform for hosting single material, multi-purpose devices. To engineer such devices, understanding electronic transport and localization across electrostatically defined interfaces is of fundamental importance. Little is known, however, about how the interplay between the band structure originating from the moire lattice and electric potential gradients affects electronic confinement. Here, we electrostatically define a cavity across a twisted double bilayer graphene sample. We observe two kinds of Fabry-Perot (FP) oscillations. The first, independent of charge polarity, stems from confinement of electrons between dispersive-band/flat-band interfaces. The second arises from junctions between regions tuned into different flat bands. When tuning the out-of-plane electric field across the device, we observe Coulomb blockade resonances in transport. This is an indication of strong electronic confinement. From the gate, magnetic field and source-drain voltage dependences of the resonances, we conclude that quantum dots form at the interfaces of the FP cavity. Our results constitute a first step toward better understanding interfacial phenomena in single crystal moire devices.