Interaction-driven quantum Hall wedding cake–like structures in graphene quantum dots

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Science  24 Aug 2018:
Vol. 361, Issue 6404, pp. 789-794
DOI: 10.1126/science.aar2014

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An electronic wedding cake

In nanostructures such as quantum dots, spatial confinement forces electrons to assume discrete energy levels. Quantization can also occur in an external magnetic field, where electrons' energies group into so-called Landau levels (LLs). Gutiérrez et al. explored the interplay between these two mechanisms and electronic interactions in a circulator resonator made of graphene. As an external magnetic field was increased, the electron quantum states transformed from atomic-like states to LL-like states. Electronic interactions caused a characteristic wedding cake–like shape of electronic density at high fields.

Science, this issue p. 789


Quantum-relativistic matter is ubiquitous in nature; however, it is notoriously difficult to probe. The ease with which external electric and magnetic fields can be introduced in graphene opens a door to creating a tabletop prototype of strongly confined relativistic matter. Here, through a detailed spectroscopic mapping, we directly visualize the interplay between spatial and magnetic confinement in a circular graphene resonator as atomic-like shell states condense into Landau levels. We directly observe the development of a “wedding cake”–like structure of concentric regions of compressible-incompressible quantum Hall states, a signature of electron interactions in the system. Solid-state experiments can, therefore, yield insights into the behavior of quantum-relativistic matter under extreme conditions.

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