Fermi-arc diversity on surface terminations of the magnetic Weyl semimetal Co₃Sn₂S₂

Weyl semimetals are gapless topological materials, breaking either spatial inversion or time reversal symmetry, that host Weyl fermions in the bulk and topological Fermi arcs states on their surface. The time reversal symmetry broken Weyl semimetals are particularly attractive since they enable to study the interplay between magnetism, electron correlations, and topology. While several inversion symmetry broken Weyl semimetals have been verified experimentally, showing unambiguous evidence for a time reversal symmetry breaking Weyl semimetal is quite challenging. We used scanning tunneling spectroscopy to study the ferromagnetic semimetal Co₃Sn₂S₂ and verified spectroscopically its classification as a time-reversal symmetry-broken Weyl semimetal [1]. In my talk I will describe how we visualize the topological “Fermi arc" states using quasiparticle interference measurements and show that the measured band structure of Co₃Sn₂S₂ exhibits direct signature of time reversal symmetry breaking, induced by the magnetic order of the Co atoms. By investigating three distinct surface terminations of the sample we examined complementary aspects of the surface and bulk band structure. I will describe the various surface and bulk electronic properties we extracted from each of the terminations. In particular I will demonstrate that the three different terminations of Co₃Sn₂S₂ exhibit not only distinct Fermi-arc contours, but also distinct connectivity between the Weyl nodes. The observed Weyl node connectivity changes from intra Brillouin zone connectivity on the Sn termination to a cross Brillouin-zones on the Co termination. This has significant implication on the magneto-transport properties of the Weyl electrons. Finally, the S termination allowed us to extract the extent of the Weyl gap by following the surface state dispersion. This provides a clear demonstration of the surface bulk correspondence in Weyl semimetals.
[1] Morali et. al. Science 365, pp 1286, (2019).