Intertwined Charge and Spin Density Waves in a Topological Kagome Material

TL;DR

This study reveals intertwined charge and spin density waves in Mn$_3$Sn, a topological kagome antiferromagnet, showing temperature-dependent modulations linked to Fermi surface nesting and Weyl node annihilation.

Contribution

It uncovers a complex, temperature-dependent spin and charge ordered state in Mn$_3$Sn, combining experimental neutron and x-ray data with theoretical Fermi surface analysis.

Findings

Identification of a homogeneous spin and charge ordered state below 285 K.

Observation of temperature-dependent wave vectors and their locking at low temperatures.

Correlation of the density wave states with Fermi surface nesting and Weyl node annihilation.

Abstract

Using neutrons and x-rays we show the topological kagome antiferromagnet Mn$_3$Sn for $T<285$~K forms a homogeneous spin and charge ordered state comprising a longitudinally polarized spin density wave (SDW) with wavevector $\textbf{k}_{\beta}=k_\beta {\bf \hat{c}}$, a helical modulated version of the room temperature anti-chiral magnetic order with $\textbf{k}_{\chi}=k_\chi{\bf \hat{c}}$, and charge density waves with wave vectors $2\textbf{k}_\beta, 2\textbf{k}_\chi$, and $\textbf{k}_\beta+\textbf{k}_\chi$. Though $\textbf{k}_{\chi}$ and $\textbf{k}_\beta$ coincide for $200~{\rm K}<T<230$~K, they exhibit distinct continuous $T-$dependencies before locking to commensurate values of $\textbf{k}_{\beta} = \frac{1}{12}\textbf{c}^{*}$ and $\textbf{k}_{\chi} = \frac{5}{48}\textbf{c}^{*}$ at low$-T$. 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.