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. We report on doping-independent CR transmission in quantitative agreement with a simple scattering model including thermal phonon scattering. As a new signature of CRs, we observe Fabry-P\'erot 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.
@article{arxiv.1901.02225,
title = {A corner reflector of graphene Dirac fermions as a phonon-scattering sensor},
author = {H. Graef and Q. Wilmart and M. Rosticher and D. Mele and L. Banszerus and C. Stampfer and T. Taniguchi and K. Watanabe and J-M. Berroir and E. Bocquillon and G. Fève and E. H. T. Teo and B. Plaçais},
journal= {arXiv preprint arXiv:1901.02225},
year = {2019}
}