Direct Observation of Dirac-Electron Wedding Cakes in Graphene Quantum Dots

The ability to apply local nanometer scale gate potentials in graphene heterostructures has recently enabled the creation of quantum dot (QD) resonators inside circular p-n junction rings, where one has detailed control of electron orbits by means of spatial and magnetic confinement. In this talk, we provide the first spatial visualization of the intricate evolution of the energy spectrum, and corresponding wavefunctions, as we condense the QD atomic-like shell states into quantized Landau levels (LLs) in a circular graphene QD. The resonator states are observed to condense into LLs beginning in the resonator center and then progressing to become edge states at the QD boundaries. The formation of compressible and incompressible rings due to Coulomb interactions inside the resonator are observed in detailed spectroscopic mapping at higher magnetic fields where the screened potential develops a prominent wedding cake-like structure. Surprisingly, the inclusion of electron interactions are found to be necessary to describe even very weak field behavior, demonstrating the importance of electron interactions in confined graphene systems.