Electron-Doping-Enhanced High-temperature Superconductivity in (3,0) Carbon Nanotube

Carbon-based materials provide a fertile ground for exploring emergent quantum phenomena. Recently, three-dimensional networks of ultrathin (3,0) and (2,1) carbon nanotubes (CNTs) confined in zeolite pores have been experimentally reported to exhibit room-temperature superconductivity. Given the instability of the (2,1) CNT, we perform first-principles calculations of superconductivity in (3,0) CNT. The predicted superconducting transition temperature (T_c) of the pristine (3,0) CNT is 18.8 K, and Li doping further increases T_c to 25.7 K. Remarkably, electron doping at 0.5 e/cell enhances the density of states and induces significant phonon softening, raising T_c to 45.6 K, exceeding the McMillan limit and surpassing several reported CNT-based superconductors, although it still can not achieve the experimentally reported room-temperature superconductivity. This work advances understanding of superconductivity in one-dimensional carbon materials and suggests a route toward high-T_c superconductivity in carbon nanostructures.