Topological Fermi-arcs and Weyl node connectivity in the ferromagnetic Weyl semimetal Co₃Sn₂S₂

Topological “Fermi-arc” surface states are guaranteed to exist on certain surfaces of Weyl semimetals. They connect the surface projection of the bulk Weyl nodes. However, in the presence of multiple pairs of surface projected Weyl nodes the actual connectivity among them is ambiguous. We use scanning tunneling spectroscopy to verify the classification of ferromagnetic Co₃Sn₂S₂ as a Weyl semimetal as well as its time reversal broken origin. By studying three different surface terminations we show that Fermi arc connectivity and Fermi-arc contour in Co₃Sn₂S₂ changes with the specific surface potential. While on the Sn surface we find intra-Brillouin zone connectivity, on the Co surface the Fermi arcs connect Weyl nodes across the Brillouin zone edge. On the S termination the Fermi–arcs hybridise with non-topological bulk and surface states thus obscuring their connectivity.