One of the hallmarks of Weyl semi-metals is the existence of unusual topological surface states known as 'Fermi arcs'. The formation of these states is guaranteed by the existence of bulk Weyl points with opposite chirality. I will present our recent findings on two types of Weyl semimetals: the non-centrosymmetric Weyl semimetal TaAs and the candidate magnetic Weyl Semimetal GdPtBi. The surface of tantalum arsenide, similar to that of other members of the Weyl semimetal class, hosts non-topological states that obscure the exploration of the Fermi arc states. We use the spatial structure of the surface states’ wave function to distinguish the surface Fermi arcs and to visualize their unique properties and their correspondence with the bulk states . We find that in contrast to non-topological surface states, the Fermi-arc wavefunction is weakly affected by the surface potential: it spreads rather uniformly within the unit cell, and penetrates deeper into the bulk. We find that the arcs’ energy dispersion shows clear correspondence with the Weyl nodes. I will show how we extract from quasi particle interference information about the structure of the Bloch wave function and how we use this information to distinguish between topological and non topological states. We further visualize magnetic response in GdPtBi in which Weyl cones and Fermi arcs are predicted to form under the application of magnetic field.
 1. R. Batabyal et al., Science Advances 2, e1600709 (2016)