Weyl fermions in ferromagnetic high-temperature phase of K2Cr8O16

By combining first-principles calculations and symmetry arguments, we propose that the half-metallic phase of K(2)Cr(8)O(16)presents ferromagnetic Weyl fermions. In particular, K(2)Cr(8)O(16)possesses two pairs of Weyl nodes, which originate from two groups of nodal lines connected by the mirror reflection symmetry. We show that the non-trivial topological properties of K(2)Cr(8)O(16)come from the partially occupied t(2g)states of Cr, and we also demonstrate that such exotic topological feature is robust. The topological surface states and corresponding Fermi arcs are revealed. As K(2)Cr(8)O(16)is a realistic and widely studied material, our results suggest that K(2)Cr(8)O(16)is an ideal candidate for studying ferromagnetic Weyl fermions. In addition, K(2)Cr(8)O(16)possesses several interesting phenomena, such as the co-existence of charge density wave and Weyl fermions, even pairs of FM Weyl points, and tunable distribution of Weyl points, which will attract intensive attentions in this field.