Chiral magnetic “particles” found in a kagome metal

Scientific Achievement

Chiral excitations in the kagome layers of TbMn6Sn6, observed with inelastic neutron scattering (INS), behave like

chiral magnetic
(Top) Schematic picture of flat-band and chiral quasiparticles  in a ferromagnetic kagome layer of TbMn6Sn6. (Bottom) Localized chiral quasiparticle (black arrows) identified by the momentum dependence of the neutron scattering data.

localized magnetic quasiparticles.

Significance and Impact

Kagome metals are platforms for a variety of charge and magnetic instabilities.  In TbMn6Sn6, strong ferromagnetism exists in the Mn kagome layers, yet we find vortex-like chiral magnetic excitations can emerge. These chiral ”particles” are not predicted from magnetic modeling, signaling new physics.

Research Details

  • INS measurements were performed at the ARCS spectrometer at the SNS.
  • High energy magnetic excitations are very broad in energy and momentum.
  • Analysis of their momentum dependence reveals two localized excitations: a “flat-band” magnon and a novel chiral excitation.
  • Localized flat-band modes are expected from modeling, whereas the chiral modes are unexpected and truly anomalous. Both modes have a metallic-like character due to hybridization with conduction electrons.
  • Chiral modes can be observed from 180 meV down to 30 meV or lower, suggesting that the FM kagome layer is close to a chiral instability.
     

S. X. M. Riberolles, et al., Chiral and flat-band magnetic quasiparticles in ferromagnetic and metallic kagome layers. Nat. Comm. 15, 1592 (2024). https://doi.org/10.1038/s41467-024-45841-8.