Metasurface electron optics in graphene
For electron optics in graphene, the propagation effect has so far been the only physical mechanism available. The resulting electron-optics-based components are large in size and operate at low temperatures to avoid violating the ballistic transport limits. In this paper, Dirac fermion metasurfaces, electronic counterparts of optical metasurfaces, are introduced for graphene electronics. By a metasurface, formally a linear array of gate-bias-controlled circular quantum dots, the wavefront of electron beams can be shaped within a one-quantum-dot-diameter distance, far below the ballistic limits at room temperature. This provides opportunities to create electron-optics-based devices that operate under ambient conditions. Moreover, unlike optical metasurfaces, Dirac fermion metasurfaces have near-perfect operating efficiencies and their high tunability allows for free and fast switching among functionalities. The concept of metasurface electron optics might open up a promising avenue for improving the performance of quantum devices in Dirac fermion materials.