Creating and Probing Electron Whispering Gallery Modes in Graphene

TL;DR

This paper demonstrates a novel method to create and probe electron whispering gallery modes in graphene using gate-tunable pn-junctions induced by a scanning tunneling probe, enabling new electronic resonator applications.

Contribution

It introduces a new approach to electron confinement in graphene via tunable whispering gallery modes using circular pn-junctions, expanding quantum electron-optics tools.

Findings

Resonant modes observed in tunneling spectra due to Klein scattering.

Resonator size and carrier concentration tunable in situ.

Potential for developing electronic lenses and resonators.

Abstract

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.