Dirac fermions and flat bands in the ideal kagome metal FeSn

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Abstract
A kagome lattice of 3d transition metal ions is a versatile platform for correlated topological phases hosting symmetry-protected electronic excitations and magnetic ground states. However, the paradigmatic states of the idealized two-dimensional kagome lattice—Dirac fermions and flat bands—have not been simultaneously observed. Here, we use angle-resolved photoemission spectroscopy and de Haas–van Alphen quantum oscillations to reveal coexisting surface and bulk Dirac fermions as well as flat bands in the antiferromagnetic kagome metal FeSn, which has spatially decoupled kagome planes. Our band structure calculations and matrix element simulations demonstrate that the bulk Dirac bands arise from in-plane localized Fe-3d orbitals, and evidence that the coexisting Dirac surface state realizes a rare example of fully spin-polarized two-dimensional Dirac fermions due to spin-layer locking in FeSn. The prospect to harness these prototypical excitations in a kagome lattice is a frontier of great promise at the confluence of topology, magnetism and strongly correlated physics.
Funding Information
  • National Science Foundation (DMR-1231319, DMR-1231319, DMR-1231319, DMR-1644779, 1541959, DMR-1231319)
  • U.S. Department of Energy (Science at 100 T, Science at 100 T, DE-AC02-98CH10886, DE-AC02-98CH10886)
  • Deutsche Forschungsgemeinschaft (SFB 1143, project A5, SFB 1143, project A5)
  • Alfred P. Sloan Foundation
  • Gordon and Betty Moore Foundation (GBMF3848)
  • United States Department of Defense | United States Army | U.S. Army Research, Development and Engineering Command | Army Research Office (W911NF-16-1-0034)

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