Interaction-driven quantum Hall wedding cake-like structures in graphene quantum dots
Christopher Gutierrez, Daniel T. Walkup, Fereshte Ghahari Kermani, Cyprian Lewandowski, Joaquin R. Nieva, Kenji Watanabe, Takashi Taniguchi, Leonid Levitov, Nikolai B. Zhitenev, Joseph A. Stroscio
Interactions amongst relativistic particles underpin exotic behaviours in diverse systems ranging from quark-gluon plasmas to Dirac electron fluids in solids. Despite long-standing interest, direct observation of quantum-relativistic matter under ambient conditions was achieved only recently through applying STM probes to graphene. The ease with which external electric and magnetic fields can be introduced in graphene provides a unique opportunity to create a table-top analogue of a strongly confined relativistic matter. Here, through a detailed spectroscopic mapping, we provide the first spatial visualization of the interplay between electric and magnetic confinement. We directly observe condensation of the orbitals of an effective many-electron "atom" into an intricate family of concentric compressible and incompressible density rings developing at high magnetic fields. The rings, resembling a wedding cake, serve as a probe of strong interactions in the system. Since the dimensionless electron-electron interaction strength in graphene is close to that in quark-gluon plasmas (1, 2), solid-state experiments can yield unique insights into the behaviour of quantum- relativistic matter under extreme conditions.