title: Topological Magnon Bands in a Kagome Lattice Ferromagnet.
abstract: There is great interest in finding materials possessing quasiparticles with topological properties. Such materials may have novel excitations that exist on their boundaries which are protected against disorder. We report experimental evidence that magnons in an insulating kagome ferromagnet can have a topological band structure. 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 that the measured band structure follows from a simple Heisenberg Hamiltonian with a Dzyaloshinkii-Moriya interaction. This serves as the first realization of an effectively two-dimensional topological magnon insulator--a new class of magnetic material that should display both a magnon Hall effect and protected chiral edge modes.
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.|NIST Center for Neutron Research, Gaithersburg, Maryland 20899, USA.
authors.forename: R
authors.initials: R
authors.lastname: Chisnell
authors.affiliation: NIST Center for Neutron Research, Gaithersburg, Maryland 20899, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Helton
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.|Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: D E
authors.initials: DE
authors.lastname: Freedman
authors.affiliation: Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA.
authors.forename: D K
authors.initials: DK
authors.lastname: Singh
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX Oxfordshire, United Kingdom.
authors.forename: R I
authors.initials: RI
authors.lastname: Bewley
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.|Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: D G
authors.initials: DG
authors.lastname: Nocera
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.|Department of Applied Physics and Department of Photon Science, Stanford University and SLAC National Accelerator Laboratory, Stanford, California 94305, USA.
authors.forename: Y S
authors.initials: YS
authors.lastname: Lee