Topological flat bands in frustrated kagome lattice CoSn

Mingu Kang, Shiang Fang, Linda Ye, Hoi Chun Po, Jonathan Denlinger, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Efthimios Kaxiras, Joseph G. Checkelsky and Riccardo Comin ()
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Mingu Kang: Massachusetts Institute of Technology
Shiang Fang: Harvard University
Linda Ye: Massachusetts Institute of Technology
Hoi Chun Po: Massachusetts Institute of Technology
Jonathan Denlinger: E. O. Lawrence Berkeley National Laboratory
Chris Jozwiak: E. O. Lawrence Berkeley National Laboratory
Aaron Bostwick: E. O. Lawrence Berkeley National Laboratory
Eli Rotenberg: E. O. Lawrence Berkeley National Laboratory
Efthimios Kaxiras: Harvard University
Joseph G. Checkelsky: Massachusetts Institute of Technology
Riccardo Comin: Massachusetts Institute of Technology

Nature Communications, 2020, vol. 11, issue 1, 1-9

Abstract: Abstract Electronic flat bands in momentum space, arising from strong localization of electrons in real space, are an ideal stage to realize strongly-correlated phenomena. Theoretically, the flat bands can naturally arise in certain geometrically frustrated lattices, often with nontrivial topology if combined with spin-orbit coupling. Here, we report the observation of topological flat bands in frustrated kagome metal CoSn, using angle-resolved photoemission spectroscopy and band structure calculations. Throughout the entire Brillouin zone, the bandwidth of the flat band is suppressed by an order of magnitude compared to the Dirac bands originating from the same orbitals. The frustration-driven nature of the flat band is directly confirmed by the chiral d-orbital texture of the corresponding real-space Wannier functions. Spin-orbit coupling opens a large gap of 80 meV at the quadratic touching point between the Dirac and flat bands, endowing a nonzero Z2 invariant to the flat band. These findings demonstrate that kagome-derived flat bands are a promising platform for novel emergent phases of matter at the confluence of strong correlation and topology.

Date: 2020
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DOI: 10.1038/s41467-020-17465-1

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