  The spin-orbit coupling (SOC) lifts the band degeneracy that plays a vital
role in the search for different topological states, such as topological
insulators (TIs) and topological semimetals (TSMs). In TSMs, the SOC can
partially gap a degenerate nodal line, leading to the formation of Dirac/Weyl
semimetals (DSMs/WSMs). However, such SOC-induced gap structure along the nodal
line in TSMs has not yet been systematically investigated experimentally. Here,
we report a direct observation of such gap structure in a magnetic WSM Co3Sn2S2
using high resolution angle-resolved photoemission spectroscopy. Our results
not only reveal the existence and importance of the strong SOC effect in the
formation of the WSM phase in Co3Sn2S2, but also provide insights for the
understanding of its exotic physical properties.
