A corner reflector of graphene Dirac fermions as a phonon-scattering sensor
Dirac fermion optics exploits the refraction of chiral fermions across optics-inspired Klein-tunneling barriers defined by high-transparency p-n junctions. We consider the corner reflector (CR) geometry introduced in optics or radars. We fabricate Dirac fermion CRs using bottom-gate-defined barriers in hBN-encapsulated graphene. By suppressing transmission upon multiple internal reflections, CRs are sensitive to minute phonon scattering rates. Here we report on doping-independent CR transmission in quantitative agreement with a simple scattering model including thermal phonon scattering. As a signature of CRs, we observe Fabry-Pérot oscillations at low temperature, consistent with single-path reflections. Finally, we demonstrate high-frequency operation which promotes CRs as fast phonon detectors. Our work establishes the relevance of Dirac fermion optics in graphene and opens a route for its implementation in topological Dirac matter.Dirac fermion optics leverages p-n junctions and Klein tunnelling barriers present in materials to implement complex optical functions and devices, including reflectors, collimators, and Dirac fermion microscopes. Here, the authors fabricate Dirac fermion corner reflectors using bottom-gate-defined barriers in hBN-encapsulated graphene, and demonstrate high-frequency operation.