28 research outputs found
Creating and Probing Electron Whispering Gallery Modes in Graphene
Designing high-finesse resonant cavities for electronic waves faces
challenges due to short electron coherence lengths in solids. Previous
approaches, e.g. the seminal nanometer-sized quantum corrals, depend on careful
positioning of adatoms at clean surfaces. Here we demonstrate an entirely
different approach, inspired by the peculiar acoustic phenomena in whispering
galleries. Taking advantage of graphene's unique properties, namely
gate-tunable light-like carriers, we create Whispering Gallery Mode (WGM)
resonators defined by circular pn-junctions, induced by a scanning tunneling
probe. We can tune the resonator size and the carrier concentration under the
probe in a back-gated graphene device over a wide range, independently and in
situ. The confined modes, revealed through characteristic resonances in the
tunneling spectrum, originate from Klein scattering at pn junction boundaries.
The WGM-type confinement and resonances are a new addition to the quantum
electron-optics toolbox, paving the way to real-world electronic lenses and
resonators
Interaction Driven Quantum Hall Wedding cake-like Structures in Graphene Quantum Dots
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
table-top prototype of strongly confined relativistic matter. Here, through a
detailed spectroscopic mapping, we provide a spatial visualization of the
interplay between spatial and magnetic confinement in a circular graphene
resonator. We directly observe the development of a multi-tiered "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 behaviour of
quantum-relativistic matter under extreme conditions