Topological Magnon Bands in Kagome Lattice Ferromagnet
Robin Michael Daub Chisnell, Joel Helton, D. E. Freedman, D. K. Singh, R. I. Bewley, D. G. Nocera, Y. S. Lee
The success of band theory in describing the motion of quantum particles inside solids is a foundational accomplishment in modern physics. Recent excitement has centered on systems for which the bands are topological. Such materials possess novel excitations that exist on their boundaries which are protected against disorder. If the bulk bands are also flat, the system can display unprecedented behavior, such as the fractional quantum Hall effect. We report experimental evidence for a new type of quasiparticle that exhibits a topological band structure: magnons (spin wave excitations) in an insulating ferromagnet. Our neutron scattering measurements further reveal that one of the bands is flat due to the unique geometry of the kagome lattice. Spin wave calculations show how the band structure follows from a surprisingly simple spin Hamiltonian. This serves as the first realization of a topological magnon insulator -- a new class of magnetic material that should display both a magnon Hall effect and protected chiral edge modes, which may be useful in spintronics applications.
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Topological Magnon Bands in Kagome Lattice Ferromagnet, Physical Review Letters, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=917818
(Accessed June 9, 2023)