Abstract
Flat electronic bands, where interactions among electrons overwhelm their kinetic energies, hold the promise for exotic correlation physics. The dice lattice has long been theorized as a host of flat bands with intriguing band topology. However, to date, no material has ever been found to host the characteristic flat bands of a dice lattice. Here, using angle-resolved photoemission spectroscopy (ARPES), we discover a dice-lattice flat band at EF in the van der Waals (vdW) electride [YCl]2+: 2e-. In this system, excess valence electrons from Y deconfine from the cation framework to form an interstitial anionic electron lattice that constitutes the dice lattice. Our ARPES measurements unambiguously identify two sets of dice-lattice bands in YCl, including a nearly dispersionless band at the Fermi level. The near-EF electronic structure observed in ARPES, which consists of the flat bands and other dispersive band features, find excellent agreement with first-principles calculations and is well captured by a simple dice-lattice model. Our findings thus end the long quest of a real dice flat band material and establish vdW electride YCl as a prototype of dice metals. Our results further demonstrate the anionic electron lattice as a novel scheme for realizing lattice geometries and electronic structures rare to find in conventional crystalline systems.
Data availability
The data that support the findings of this study are available from the corresponding authors on reasonable request.
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Acknowledgements
This work was supported by NSFC-Young Scientists Fund (No. 12304093, No. 12504194 and No. 12447158), Guangdong Natural Science Fund-General Program (No. 2025A1515010667), the Guangdong Provincial Quantum Science Strategic Initiative (Grant No. GDZX2501004) and Start-up Fund of HKUST(GZ) through grant no. G0101000127 and no. G0104000263. The Modern Matter Laboratory (MML), Green e Materials Laboratory (GeM), and the Materials Characterization and Preparation Facility (MCPF) at HKUST(GZ) provided the necessary instruments for the crystal synthesis and characterizations. We acknowledge beamline I05 at Diamond Light Source for beamtime under proposal SI38254.
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S.G., B.T.Z., and H.Li conceived the project. S.G. and H.Li led the ARPES measurement and analysis. R.G., X.W., F.C., Q.W., K.L., P.H., Y.W., S.C., Z.S., T.K., C.C., and D.D. helped with the ARPES measurement. X.W., R.G., S.G., Y.H., and H.Li performed the single-crystal synthesis and the crystal characterizations. S.G., H.Li, and B.T.Z. carried out the DFT and TB model calculations. D.D., H.Liang, and C.Q. helped to give suggestions. S.G., B.T.Z., and H.Li did the majority of the paper writing, with contributions from all coauthors. B.T.Z. and H.Li directed the overall project.
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Geng, S., Wang, X., Guo, R. et al. Experimental realization of dice-lattice flat band at the Fermi level in layered electride YCl. Nat Commun (2026). https://doi.org/10.1038/s41467-026-69049-0
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DOI: https://doi.org/10.1038/s41467-026-69049-0
