# A corner reflector of graphene Dirac fermions as a phonon-scattering sensor

## TL;DR

This paper demonstrates a graphene-based corner reflector that uses Dirac fermion optics to detect phonon scattering with high sensitivity, showing potential for fast phonon detection and applications in topological Dirac materials.

## Contribution

It introduces a novel corner reflector design in graphene that leverages Dirac fermion optics to sense phonon scattering, including experimental validation and high-frequency operation.

## Key findings

- CRs are sensitive to minute phonon scattering rates.
- Doping-independent CR transmission matches a simple scattering model.
- Fabry-Pérot oscillations observed at low temperature.

## Abstract

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.