Valley filtering and electronic optics using polycrystalline graphene
  In this Letter, both the manipulation of valley-polarized currents and the optical-like behaviors of Dirac fermions are theoretically explored in polycrystalline graphene. When strain is applied, the misorientation between two graphene domains separated by a grain boundary can result in a mismatch of their electronic structures. Such a discrepancy manifests itself in a strong breaking of the inversion symmetry, leading to perfect valley polarization in a wide range of transmission directions. In addition, these graphene domains act as different media for electron waves, offering the possibility to modulate and obtain negative refraction indexes. 
Viet Hung Nguyen, Samuel Dechamps, Philippe Dollfus, and   Jean-Christophe Charlier
cond-mat.mes-hall