Massive Dirac fermions in a ferromagnetic kagome metal

• Published in: Nature (London) 2018-03, Vol.555 (7698), p.638-642
• Main Authors: Ye, Linda, Kang, Mingu, Liu, Junwei, von Cube, Felix, Wicker, Christina R., Suzuki, Takehito, Jozwiak, Chris, Bostwick, Aaron, Rotenberg, Eli, Bell, David C., Fu, Liang, Comin, Riccardo, Checkelsky, Joseph G.
• Format: Article
• Language: English
• Subjects: 140/146; 639/766/119/2792; 639/766/119/2793; 639/766/119/995; Antiferromagnetism; Broken symmetry; Conductivity; Cones; Curvature; Electromagnetism; Electron states; Electronic properties; Fermions; Ferromagnetism; Humanities and Social Sciences; Kagome lattice; Lattices; letter; Magnetic properties; multidisciplinary; Photoelectric emission; Science; Spectroscopy; Spectrum analysis; Spin-orbit interactions; Subatomic particles; Symmetry; Triangles
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature25987

Fe 3 Sn 2 hosts massive Dirac fermions, owing to the underlying symmetry properties of the bilayer kagome lattice in the ferromagnetic state and the atomic spin–orbit coupling. Dirac fermions found in a kagome lattice The kagome lattice consists of vertices and edges of trihexagonal tiling, whereby each hexagon is surrounded by triangles, creating a two-dimensional network of corner-sharing triangles. Materials that exhibit the kagome lattice have long been studied in the context of quantum spin liquids, but they are also predicted to host Dirac points in a manner similar to the hexagonal graphene lattice. Unlike graphene, however, strong electronic correlations could have a role and, with ferromagnetic ordering also possible, a range of exotic correlated topological phases could emerge. Joseph Checkelsky and colleagues now provide evidence that the bilayer kagome and ferromagnetic metal compound Fe 3 Sn 2 hosts quasi-two-dimensional massive Dirac electrons, which acquire a correlated topological character. This material provides an interesting platform in the search for emergent states of matter at the confluence of correlations and topology. The kagome lattice is a two-dimensional network of corner-sharing triangles 1 that is known to host exotic quantum magnetic states 2 , 3 , 4 . Theoretical work has predicted that kagome lattices may also host Dirac electronic states 5 that could lead to topological 6 and Chern 7 insulating phases, but these states have so far not been detected in experiments. Here we study the d -electron kagome metal Fe 3 Sn 2 , which is designed to support bulk massive Dirac fermions in the presence of ferromagnetic order. We observe a temperature-independent intrinsic anomalous Hall conductivity that persists above room temperature, which is suggestive of prominent Berry curvature from the time-reversal-symmetry-breaking electronic bands of the kagome plane. Using angle-resolved photoemission spectroscopy, we observe a pair of quasi-two-dimensional Dirac cones near the Fermi level with a mass gap of 30 millielectronvolts, which correspond to massive Dirac fermions that generate Berry-curvature-induced Hall conductivity. We show that this behaviour is a consequence of the underlying symmetry properties of the bilayer kagome lattice in the ferromagnetic state and the atomic spin–orbit coupling. This work provides evidence for a ferromagnetic kagome metal and an example of emergent topological electronic properties in a correlated el