Intraband electron focusing in bilayer graphene
  We propose an implementation of a valley selective electronic Veselago lens in bilayer graphene. We demonstrate that in the presence of an appropriately oriented potential step, low-energy electrons radiating from a point source can be re-focused coherently within the same band. The phenomenon is due to the trigonal warping of the band structure that leads to a negative refraction index. We show that the interference pattern can be controlled by an external mechanical strain. 
Csaba G. P\'eterfalvi, L\'aszl\'o Oroszl\'any, Colin J. Lambert,   J\'ozsef Cserti
cond-mat.mes-hall