Intertwined charge and spin density waves in a topological kagome material

Abstract

Using neutrons and x rays we show the topological kagome antiferromagnet Mn_{3}Sn for T<285K forms a homogeneous spin and charge ordered state comprising a longitudinally polarized spin density wave with wave vector k_{β}=k_{β}c[over ̂], a helical modulated version of the room temperature antichiral magnetic order with k_{χ}=k_{χ}c[over ̂], and charge density waves with wave vectors 2k_{β},2k_{χ}, and k_{β}+k_{χ}. Though k_{χ} and k_{β} coincide for 200K<T<230K, they exhibit distinct continuous Tdependencies before locking to commensurate values of k_{β}=1/12c^{*} and k_{χ}=5/48c^{*} at lowT. Density functional theory indicates this complex modulated state may be associated with the nesting of Fermi surfaces from correlated flat kagome bands, which host Weyl nodes that are annihilated as it forms.