title: Weyl magnons in breathing pyrochlore antiferromagnets.
abstract: Frustrated quantum magnets not only provide exotic ground states and unusual magnetic structures, but also support unconventional excitations in many cases. Using a physically relevant spin model for a breathing pyrochlore lattice, we discuss the presence of topological linear band crossings of magnons in antiferromagnets. These are the analogues of Weyl fermions in electronic systems, which we dub Weyl magnons. The bulk Weyl magnon implies the presence of chiral magnon surface states forming arcs at finite energy. We argue that such antiferromagnets present a unique example, in which Weyl points can be manipulated in situ in the laboratory by applied fields. We discuss their appearance specifically in the breathing pyrochlore lattice, and give some general discussion of conditions to find Weyl magnons, and how they may be probed experimentally. Our work may inspire a re-examination of the magnetic excitations in many magnetically ordered systems.
authors.affiliation: Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
authors.forename: Fei-Ye
authors.initials: FY
authors.lastname: Li
authors.affiliation: School of Computer Science, Fudan University, Shanghai 200433, People's Republic of China.
authors.forename: Yao-Dong
authors.identifier: 0000-0003-3742-1944
authors.initials: YD
authors.lastname: Li
authors.affiliation: Department of Physics, University of Toronto, Canadian Institute for Advanced Research, Quantum Materials Program, Toronto, Ontario, Canada MSG1Z8.|School of Physics, Korea Institute for Advanced Study, Seoul 130-722, Korea.
authors.forename: Yong Baek
authors.initials: YB
authors.lastname: Kim
authors.affiliation: Kavli Institute for Theoretical Physics, Santa Barbara, California 93106, USA.
authors.forename: Leon
authors.initials: L
authors.lastname: Balents
authors.affiliation: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, People's Republic of China.|Center for Field Theory and Particle Physics, Department of Physics, Fudan University, Shanghai 200433, People's Republic of China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China.
authors.forename: Yue
authors.initials: Y
authors.lastname: Yu
authors.affiliation: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, People's Republic of China.|Center for Field Theory and Particle Physics, Department of Physics, Fudan University, Shanghai 200433, People's Republic of China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China.
authors.forename: Gang
authors.initials: G
authors.lastname: Chen