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Published January 14, 2022 | Submitted
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Ascendance of Superconductivity in Magic-Angle Graphene Multilayers

Abstract

Graphene moire superlattices have emerged as a platform hosting and abundance of correlated insulating, topological, and superconducting phases. While the origins of strong correlations and non-trivial topology are shown to be directly linked to flat moire bands, the nature and mechanism of superconductivity remain enigmatic. In particular, only alternating twisted stacking geometries of bilayer and trilayer graphene are found to exhibit robust superconductivity manifesting as zero resistance and Fraunhofer interference patterns. Here we demonstrate that magic-angle twisted tri-, quadri-, and pentalayers placed on monolayer tungsten diselenide exhibit flavour polarization and superconductivity. We also observe insulating states in the trilayer and quadrilayer arising at finite electric displacement fields, despite the presence of dispersive bands introduced by additional graphene layers. Moreover, the three multilayer geometries allow us to identify universal features in the family of graphene moire structures arising from the intricate relations between superconducting states, symmetry-breaking transitions, and van Hove singularities. Remarkably, as the number of layers increases, superconductivity emerges over a dramatically enhanced filling-factor range. In particular, in twisted pentalayers, superconductivity extends well beyond the filling of four electrons per moire unit cell, demonstrating the non-trivial role of the additional bands. Our results highlight the importance of the interplay between flat and dispersive bands in extending superconducting regions in graphene moire superlattices and open new frontiers for developing graphene-based superconductors.

Additional Information

Attribution 4.0 International (CC BY 4.0). We thank Haoxin Zhou and Soudabeh Mashahadi for fruitful discussions. This work has been primarily supported by NSF-CAREER award (DMR-1753306), and Office of Naval Research (grant no. N142112635), and Army Research Office under Grant Award W911NF17-1-0323. Nanofabrication efforts have been in part supported by Department of Energy DOE-QIS program (DE-SC0019166). S.N-P. acknowledges support from the Sloan Foundation (grant no. FG-2020-13716). G.R., J.A., and S.N.-P. also acknowledge support of the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center with support of the Gordon and Betty Moore Foundation through Grant GBMF1250. C.L. acknowledges support from the Gordon and Betty Moore Foundation's EPiQS Initiative, grant GBMF8682. Y.P. acknowledges support from the startup fund from California State University, Northridge. F.v.O. is supported by CRC 183 (project C02) of Deutsche Forschungsgemeinschaft. Author Contribution: Y.Z. and R.P. performed the measurements, fabricated the devices, and analyzed the data. Y.C. and H.K. helped with device fabrication and data analysis. C.L., A.T. and Y.P. developed theoretical models and performed calculations in close collaboration and guidance by F.v.O., G.R. and J.A. K.W. and T.T. provides hBN crystals. S.N-P. supervised the project. Y.Z., R.P., C.L., A.T., Y.P., F.v.O., G.R., J.A., and S.N-P. wrote the manuscript with the input of other authors. The authors declare no competing interests. Data availability: The data supporting the findings of this study are available from the corresponding authors on reasonable request. Code availability: All code used in modeling in this study is available from the corresponding authors on reasonable request.

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Additional details

Created:
August 20, 2023
Modified:
October 23, 2023