Three-dimensional flat bands in pyrochlore metal CaNi2

Joshua P. Wakefield, Mingu Kang, Paul M. Neves, Dongjin Oh, Shiang Fang, Ryan McTigue, S. Y. Frank Zhao, Tej N. Lamichhane, Alan Chen, Seongyong Lee, Sudong Park, Jae-Hoon Park, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Anil Rajapitamahuni, Elio Vescovo, Jessica L. McChesney, David Graf, Johanna C. Palmstrom, Takehito Suzuki, Mingda Li, Riccardo Comin () and Joseph G. Checkelsky ()
Additional contact information
Joshua P. Wakefield: Massachusetts Institute of Technology
Mingu Kang: Massachusetts Institute of Technology
Paul M. Neves: Massachusetts Institute of Technology
Dongjin Oh: Massachusetts Institute of Technology
Shiang Fang: Massachusetts Institute of Technology
Ryan McTigue: Massachusetts Institute of Technology
S. Y. Frank Zhao: Massachusetts Institute of Technology
Tej N. Lamichhane: Massachusetts Institute of Technology
Alan Chen: Massachusetts Institute of Technology
Seongyong Lee: Max Planck POSTECH/Korea Research Initiative
Sudong Park: Max Planck POSTECH/Korea Research Initiative
Jae-Hoon Park: Max Planck POSTECH/Korea Research Initiative
Chris Jozwiak: Lawrence Berkeley National Laboratory
Aaron Bostwick: Lawrence Berkeley National Laboratory
Eli Rotenberg: Lawrence Berkeley National Laboratory
Anil Rajapitamahuni: Brookhaven National Laboratory
Elio Vescovo: Brookhaven National Laboratory
Jessica L. McChesney: Argonne National Laboratory
David Graf: National High Magnetic Field Laboratory
Johanna C. Palmstrom: National High Magnetic Field Laboratory, LANL
Takehito Suzuki: Toho University
Mingda Li: Massachusetts Institute of Technology
Riccardo Comin: Massachusetts Institute of Technology
Joseph G. Checkelsky: Massachusetts Institute of Technology

Nature, 2023, vol. 623, issue 7986, 301-306

Abstract: Abstract Electronic flat-band materials host quantum states characterized by a quenched kinetic energy. These flat bands are often conducive to enhanced electron correlation effects and emergent quantum phases of matter1. Long studied in theoretical models2–4, these systems have received renewed interest after their experimental realization in van der Waals heterostructures5,6 and quasi-two-dimensional (2D) crystalline materials7,8. An outstanding experimental question is if such flat bands can be realized in three-dimensional (3D) networks, potentially enabling new materials platforms9,10 and phenomena11–13. Here we investigate the C15 Laves phase metal CaNi2, which contains a nickel pyrochlore lattice predicted at a model network level to host a doubly-degenerate, topological flat band arising from 3D destructive interference of electronic hopping14,15. Using angle-resolved photoemission spectroscopy, we observe a band with vanishing dispersion across the full 3D Brillouin zone that we identify with the pyrochlore flat band as well as two additional flat bands that we show arise from multi-orbital interference of Ni d-electrons. Furthermore, we demonstrate chemical tuning of the flat-band manifold to the Fermi level that coincides with enhanced electronic correlations and the appearance of superconductivity. Extending the notion of intrinsic band flatness from 2D to 3D, this provides a potential pathway to correlated behaviour predicted for higher-dimensional flat-band systems ranging from tunable topological15 to fractionalized phases16.

Date: 2023
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DOI: 10.1038/s41586-023-06640-1

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