Fabry-P\'erot cavities and quantum dot formation at gate-defined interfaces in twisted double bilayer graphene

TL;DR

This study demonstrates electrostatically defined cavities in twisted double bilayer graphene, revealing Fabry-Pérot oscillations and quantum dot formation at interfaces, advancing understanding of electronic confinement in moiré materials.

Contribution

It provides the first experimental evidence of quantum dot formation at interfaces in twisted double bilayer graphene using electrostatic gating.

Findings

Observation of two types of Fabry-Pérot oscillations.

Detection of Coulomb blockade resonances indicating quantum dots.

Identification of interface-induced electronic confinement phenomena.

Abstract

The rich and electrostatically tunable phase diagram exhibited by moir\'e 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 moir\'e 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-P\'erot 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, an indication of strong electronic confinement. From the gate, magnetic field and source-drain voltage dependence of the resonances, we conclude that quantum dots form at the interfaces of the Fabry-P\'erot cavity. Our results constitute a first step towards better understanding interfacial phenomena in single crystal moir\'e devices.