Weyl fermions in ferromagnetic high-temperature phase of K2Cr8O16

Abstract

By combining first-principles calculations and symmetry arguments, we propose that the half-metallic phase of K2Cr8O16 presents ferromagnetic Weyl fermions. In particular, K2Cr8O16 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 K2Cr8O16 come from the partially occupied t2g 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 K2Cr8O16 is a realistic and widely studied material, our results suggest that K2Cr8O16 is an ideal candidate for studying ferromagnetic Weyl fermions. In addition, K2Cr8O16 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.