Superconductivity at 28 K in Sodium Graphite Intercalation Compound under High Pressure
Guangchen Ma1,2, Yingying Wang1,3, Zefang Wang2
1Jilin University, State Key Laboratory of High Pressure and Superhard Materials, College of Physics, Changchun 130012, China.
Physical Review Letters
|October 31, 2025
Summary
Researchers discovered superconductivity in sodium carbide (NaC8) at 28 K and 14 GPa, a significant advance for high-temperature superconductors. This finding opens new avenues for exploring superconductivity in light-element compounds.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Solid State Chemistry
Background:
- Graphite intercalation compounds (GICs) show superconductivity, with CaC6 exhibiting 15.1 K superconductivity.
- Research on high-temperature superconductivity in GICs has stagnated for nearly two decades.
- Superconductivity in high-stage GICs remains largely unexplored, with focus on first-stage compounds.
Purpose of the Study:
- To investigate superconductivity in high-stage GICs.
- To discover new high-temperature superconducting materials.
- To explore sodium carbide as a potential high-temperature superconductor.
Main Methods:
- Experimental discovery of superconductivity using resistance drop measurements.
- Magnetic field dependence studies up to 6 T.
- X-ray diffraction and crystal structure prediction.
Main Results:
- Superconductivity observed in sodium carbide at a critical temperature (Tc) of approximately 28 K and 14 GPa.
- Resistance showed a sharp drop, and Tc decreased characteristically under magnetic fields.
- The superconducting material was identified as the second-stage GIC NaC8.
- Upper critical field (μ0Hc2(0)) estimated at 8.8 T; coherence length at ~61.2 Å.
Conclusions:
- Achieved long-sought high-Tc GICs, surpassing previous records.
- Identified NaC8 as a high-stage GIC exhibiting significant superconductivity.
- Opened a new research direction for high-temperature superconductors in light-element compounds.
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