Superconductivity induced by element doping in C₄₈ fullerene at ambient pressure

To investigate the superconducting potential of cage-type carbon compounds under ambient pressure, a pristine all-carbon C₄₈ fullerene structure is designed and doped with various elements. By optimizing the occupancy of group IA, IIA, and IIIA elements at different sites within the C₄₈ framework, we have obtained both stable metallic M₂C₂₄ (M = Li, Na, Mg, Al, Ga, and In) and HC₂₄ structures. First-principles calculations demonstrate that metal atoms, serving as electron donors, can induce a semiconductor-to-metal transition in the C₂₄ clathrate, while preserving high structural rigidity with a Vickers hardness exceeding 25 GPa. Further analysis of the superconducting properties reveals that the enhanced electronic state density at the Fermi level, driven by the vibration of the rigid carbon framework and elemental doping, enables Li₂C₂₄ to exhibit a superconducting transition temperature (T_c) of 12.71 K at ambient pressure. Similarly, the doping of non-metallic hydrogen effectively tunes HC₂₄ into a superconductor with a T_c of 8.39 K. This study deepens the understanding of superconductivity in carbon cage compounds and opens new avenues for realizing high-temperature superconductors through hole doping and other modulation strategies.