Low-energy magnons in the chiral ferrimagnet Cu 2 OSeO 3: A coarse-grained approach

• Published in: Physical review. B 2020-04, Vol.101 (14)
• Main Authors: Luo, Yi, Marcus, G. G., Trump, B. A., Kindervater, J., Stone, M. B., Rodriguez-Rivera, J. A., Qiu, Yiming, McQueen, T. M., Tchernyshyov, O., Broholm, C.
• Format: Article
• Language: English
• Subjects: charge transport; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; defects; magnetism and spin physics; materials and chemistry by design; optics; quantum information science; superconductivity; synthesis (novel materials); thermal conductivity
• ISSN: 2469-9950; 2469-9969

We report a comprehensive neutron scattering study of low energy magnetic excitations in the breathing pyrochlore helimagnetic Cu2OSeO3. Fully documenting the four lowest energy magnetic modes that leave the ferrimagnetic configuration of the “strong tetrahedra” intact (| ℏ ω| < 13 meV), we find gapless quadratic dispersion at the Γ point for energies above 0.2 meV, two doublets separated by 1.6(2) meV at the R point, and a bounded continuum at the X point. Our constrained rigid spin cluster model relates these features to Dzyaloshinskii-Moriya (DM) interactions and the incommensurate helical ground state. Combining conventional spin wave theory with a spin cluster form factor accurately reproduces the measured equal time structure factor through multiple Brillouin zones. An effective spin Hamiltonian describing complex anisotropic intercluster interactions is obtained.