Zhao Liu, Xiang Wang, Yin Yang, Pengcheng Ma, Zhijun Tu, Xinyu Wang, Donghan Jia, Wenju Zhou, Huiyang Gou, Hechang Lei, Qiang Xu, Zhonghao Liu, Tian Cui
In exhibit dual anionic and near-free electron characteristics. With our established effective local potential model, we trace that IAEs are located near Fermi-level states above potential barriers, forming a Fermi sea susceptible to La-derived phonon scattering, triggering superconductivity at 9.4 K. ARPES combined with high-resolution XRD measurements on oxygen-treated samples confirms the spatial distribution and energy dispersion of IAEs, aligning with our theoretical predictions. Oxygen treatment-induced reduction of near-free electrons correlates with diminished superconductivity, directly linking IAEs to electron-phonon coupling. Our study resolves the long-standing ambiguity regarding the nature of IAEs, elucidates their role in driving phonon-mediated superconductivity, and lays the foundation for exploring electride-based superconductors.