Whispering gallery modes (WGMs) are quite common in acoustics and optics. They denote the guided waves circulating along a concave surface, the seminal example being the whispering galleries of St. Paul’s cathedral: someone whispering on one side of the gallery can be heard all along the circumference of the gallery thanks to WGMs. The optical counterparts of these WGMs resonances are already exploited in detectors sensitive to a single virus. However, they have been much less explored in electronic systems. Our contribution to the topic consisted in devising a movable circular cavity, created by the biased sharp tip of an atomic force microscope, in a graphene sheet. The cavity hosts the resonating electronic WGMs modes, which are selected and controlably coupled (or "transduced") to conducting channels in the graphene sheet by moving the tip. This work constitutes a further step towards “Dirac fermion optics”, exploiting the peculiar characteristics of massless charge carriers in graphene.
A large part of the experimental work was performed by Boris Brun, in the group of Benoit Hackens at the time of the experiments, with contributions from Christoph Stampfer's group at RWTH Aachen for the device fabrication, and Jean-Christophe Charlier's group for the simulations.