  Experiments identified Co3Sn2S2 as the first magnetic Weyl semimetal (MWSM).
Using first-principles calculation with a global optimization approach, we
explore the structural stabilities and topological electronic properties of
cobalt (Co-based shandite and alloys, Co3MM-X2 (M/M-=Ge, Sn, Pb, X=S, Se, Te),
and identify new stable structures with new Weyl phases. Using a tight-binding
model, for the first time, we reveal that the physical origin of the nodal
lines of a Co-based shandite structure is the interlayer coupling between Co
atoms in different Kagome layers, while the number of Weyl points and their
types are mainly governed by the interaction between Co and the metal atoms,
Sn, Ge, and Pb. The Co3SnPbS2 alloy exhibits two distinguished topological
phases, depending on the relative positions of the Sn and Pb atoms: a
three-dimensional quantum anomalous Hall metal, and a MWSM phase with anomalous
Hall conductivity (~1290) that is larger than that of Co2Sn2S2. Our work
reveals the physical mechanism of the origination of Weyl fermions in Co-based
shandite structures and proposes new topological quantum states with high
thermal stability.
