Electronic analog of chiral metamaterial: Helicity-resolved filtering and focusing of Dirac fermions in thin films of topological materials

Control over the helicity degree of freedom of Dirac fermions is identified in thin films of topological materials which act as a tunable "chiral-metamaterial-like" platform to tame left- and right-handed Dirac fermions in two dimensions. Using topological crystalline insulator SnTe(111) thin films as an example, we perform the first-principles calculations and show that giant helicity splitting in the band structures can be induced under moderate electric field. Based on this result, helicity-resolved functionalities, including pronounced electron dichroism, helicity switching, helical negative refraction, and birefraction, are demonstrated, where the intrahelical scattering always dominates over the interhelical one. Such intriguing control strategy for helical Dirac fermions may hold great promise for the applications of helicity-based electron optics and nanoelectronics.