Weyl magnons in breathing pyrochlore antiferromagnets

• Published in: Nature communications Vol. 7; no. 1; p. 12691
• Main Authors: Li, Fei-Ye, Li, Yao-Dong, Kim, Yong Baek, Balents, Leon, Yu, Yue, Chen, Gang
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 21.09.2016; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/119/2792; 639/766/119/995; 639/766/119/997; Anisotropy; Electronic properties and materials; Humanities and Social Sciences; Magnetic properties and materials; MATERIALS SCIENCE; Microscopy; multidisciplinary; Pallets; Physics; Science; Science (multidisciplinary); Theoretical physics; Topological insulators; China
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms12691

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. It was recently demonstrated that particular materials with non-trivial electronic band structure support quasiparticle excitations described by the relativistic Weyl equation. Here, the authors explore how an analogous magnonic band structure may exist in breathing pyrochlore antiferromagnets.