Abstract
The coexistence of correlated electron and hole crystals enables the realization of quantum excitonic states, capable of hosting counterflow superfluidity and topological orders with long-range quantum entanglement. Here we report evidence for imbalanced electron–hole crystals in a doped Mott insulator, namely, α-RuCl3, through gate-tunable non-invasive van der Waals doping from graphene. Real-space imaging via scanning tunnelling microscopy reveals two distinct charge orderings at the lower and upper Hubbard band energies, whose origin is attributed to the correlation-driven honeycomb hole crystal composed of hole-rich Ru sites and rotational-symmetry-breaking paired electron crystal composed of electron-rich Ru–Ru bonds, respectively. Moreover, a gate-induced transition of electron–hole crystals is directly visualized, further corroborating their nature as correlation-driven charge crystals. The realization and atom-resolved visualization of imbalanced electron–hole crystals in a doped Mott insulator opens new doors in the search for correlated bosonic states within strongly correlated materials.
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Acknowledgements
J. Lu acknowledges support from Ministry of Education grants (MOE-T2EP50121-0008, MOE-T2EP10221-0005, MOE-T2EP10123-0004) and Agency for Science, Technology and Research (A*STAR) under its AME IRG Grant (M21K2c0113). K.S.N. acknowledges support from the Ministry of Education, Singapore (Research Centre of Excellence award to the Institute for Functional Intelligent Materials (I-FIM) project no. EDUNC-33-18-279-V12), and the Royal Society, UK (grant no. RSRP\R\190000). M.K. acknowledges support from the Russian Science Foundation (grant no. 21-79-20225) and Vladimir Potanin (through Brain and Consciousness Research Center).
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J. Lu supervised the project and organized the collaborations. Z.Q. performed the STM measurements and analysed the results. Z.Q., Y.H., K.S.N., J. Lu and A.H.C.N. devised the model to account for the two charge orderings. Z.C., M.K. and K.S.N. contributed to the sample and device fabrication. Y.H. and H.F. assisted in the STM measurements. J. Li, L.L. and P.L. helped in preparing the sample. K.N., S.Y.Q. and A.R. calculated the electronic band structure and charge transfer. T.O. calculated the electronic band structure and the Fermi surface contour. X.G., S.A. and A.H.C.N. contributed to the discussion of the theoretical model for strongly correlated α-RuCl3. M.T. helped with the N+ implantation. All authors contributed to the scientific discussion. Z.Q., K.S.N. and J. Lu co-wrote the manuscript with input from all authors.
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Qiu, Z., Han, Y., Noori, K. et al. Evidence for electron–hole crystals in a Mott insulator. Nat. Mater. (2024). https://doi.org/10.1038/s41563-024-01910-3
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DOI: https://doi.org/10.1038/s41563-024-01910-3
