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Superconductivity at 28 K in Sodium Graphite Intercalation Compound under High Pressure

Guangchen Ma1,2,*, Yingying Wang1,3,*, Zefang Wang2,*, Yuki Nakamoto4, Katsuya Shimizu4, Guangtao Liu2, Mi Zhou2, Hongbo Wang1,2,†, Pengyue Gao2,‡ et al.

Yanming Ma5,1,2,6,§

  • 1State Key Laboratory of High Pressure and Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
  • 2Key Laboratory of Material Simulation Methodsand Software of Ministry of Education, College of Physics, Jilin University, Changchun 130012, China
  • 3School of Physics and Electronic Engineering, Qilu Normal University, Jinan 250200, China
  • 4Center for Science and Technology under Extreme Conditions, Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan
  • 5School of Physics, Zhejiang University, Hangzhou 310027, China
  • 6International Center of Future Science, Jilin University, Changchun 130012, China

  • *These authors contributed equally to this work.
  • †Contact author: whb2477@jlu.edu.cn
  • ‡Contact author: gpy@calypso.cn
  • §Contact author: mym@jlu.edu.cn
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Phys. Rev. Lett. 135, 166003 – Published 15 October, 2025

DOI: https://doi.org/10.1103/2t6l-sqmj

Abstract

The discovery of 15.1 K superconductivity in first-stage CaC6 reignited interest in searching for high-temperature superconductors in graphite intercalation compounds (GICs). However, despite nearly two decades of intensive research, progress in exploring high-temperature superconductivity in GIC materials has remained stagnant. Currently, research on the superconductivity of GICs mainly focuses on first-stage GICs, while the superconductivity of high-stage GICs has been largely overlooked. Here, we report an experimental discovery of superconductivity with maximum critical temperature (Tc) of approximately 28 K in sodium carbide at about 14 GPa evidenced by a sharp drop of resistance and a characteristic decrease of Tc under magnetic fields up to 6 T. The upper critical field μ0Hc2(0) was estimated to be 8.8 T based on fitting with the Ginzburg-Landau superconducting model while the coherent length is approximately 61.2  Å. X-ray diffraction measurements combined with crystal structure predictions identified the superconducting candidate material as the second-stage GIC NaC8, in which sodium atoms occupy the interlayer spaces between AA-stacked bilayer graphene. The current findings not only achieve the long-sought high-Tc GICs, but more importantly, open up a new avenue for exploring high-temperature superconductors in light-element compounds.

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Phys. Rev. Lett. 135, 166003– Published 15 October, 2025
  • Received 3 April 2025
  • Accepted 25 September 2025
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