Sharif Digital Repository

Beenakker noticed that the peculiar band structure of Dirac fermions in two-dimensional (2D) solids allows for the specular Andreev reflection in these systems, which has no analogue in other 2D electron systems. An interesting deformation of the Dirac equation in the solid state is to tilt it, which has now been realized in materials. In this paper we report another peculiar feature of the Andreev reflection in tilted 2D Dirac cone systems. The tilt deformation of the Dirac equation is characterized by two parameters ζ=ζ(cosθ,sinθ). We show that when the tilt parameter is tuned to its "horizon value" ζ=1, irrespective of the incidence angle of electrons, the Andreev reflected hole is always... 

Using Green's function of semi-infinite Weyl semimetals, we present the quantum theory of the collective charge dynamics of Fermi arcs. We find that the Fermi arc plasmons in undoped Weyl semimetals are linearly dispersing gapless plasmon modes. The gaplessness comes from proper consideration of the deep penetration of surface states near the end of the Fermi arcs into the interior of the Weyl semimetal. The linear dispersion - rather than square root dispersion of pure 2D electron systems with extended Fermi surface - arises from the strong anisotropy introduced by the Fermi arc itself, due to which the continuum of surface particle-hole (PH) excitations in this system will have a strong...