Topological Weyl semimetals in Full Heusler Co₂MnX (X = Si, Ge, Sn)

Topological semimetals exhibit band crossing in the bulk and exotic surface states, called Fermi arcs, which are protected by topology of the associated wavefunctions. These states are characterized by their connectivity and dimensionality in the momentum space. Using first-principles calculations we show that ferromagnetic full Heusler compounds Co₂MnX (X = Si, Ge, Sn) belong to the category of topological semimetals called Weyl semimetals. Based on electronic structure calculations, we show that these materials show multiple nontrivial band crossings called Hopf links or entangled nodal lines and chain-like nodal lines, in absence of spin-orbit coupling, which are protected by mirror symmetry of the lattice. On breaking the time-reversal symmetry, we find that these band crossings are protected along multiple zero-dimensional Weyl points with different chiralities. We further explore the possibility of identifying non-trivial Fermi arc surface states connecting projection of these Weyl points on surface of opposite chiralities.