The effect of a velocity barrier on the ballistic transport of Dirac fermions

We propose a novel way to manipulate the transport properties of massless Dirac fermions by using velocity barriers, a region in which the Fermi velocity, $v_{F}$, has a value that differs from the one in the surrounding background. We find that the transmission through a velocity barrier is highly anisotropic, and that perfect transmission always occurs at normal incidence. We also analyzed consequences of such a barrier on the conductivity and Fano factors in the wide ribbon limit, and show that its effects should be easily mesurable with current available technology. Remarkably, when $v_{F}$ in the barrier is larger that the velocity outside the barrier, we find that a critical transmission angle exists, a Brewster-like angle for massless Dirac electrons. The later being the basic element to construct electron waveguides and related devices.