Fermi arc induced vortex structure in Weyl beam shifts

In periodic media, despite the close relationship between geometrical effects in the bulk and topological surface states, the two are typically probed separately. Here, we show that when beams in a Weyl medium reflect off an interface with a gapped medium, the trajectory is influenced by both bulk geometrical effects and the presence of Fermi arc surface states. The reflected beam experiences a displacement, analogous to the Goos-Hanchen or Imbert-Fedorov shifts, that forms a half-vortex in the two-dimensional surface momentum space. The half-vortex structure is centered at the point where the Fermi arc of the reflecting surface touches the Weyl cone, and the magnitude of the shift scales as the inverse square root of distance from the touching-point. This striking feature provides a way to use bulk transport to probe the topological characteristics of a Weyl medium.