Superconductivity induced by ionized σ-bond at 10 GPa

Discovering high-temperature superconductors under low pressures and elucidating the underlying critical factors governing superconductivity are central issues in condensed matter physics. Here, we developed a strategy for the metallization of σ-bonds through incorporating NH3-units into the filled f-shell Lu-lattice and obtained a Luδ+ (NH3)4σ− hydride to investigate the potential high-temperature superconductivity. Based on the density-functional theory calculations, our proposed I-43m-Luδ+ (NH3)4σ− phase exhibits a Tc of 33.44 K at 10 GPa. Further analyses unveil that the Tc is attributed to strong electron-phonon coupling (EPC), which originated from the electron-phonon matrix element primarily driven by H–N–H bending and twisting vibrations, and Fermi surface nesting induced softening of optical phonons to scatter itinerant electrons on phonon-coupling bands to form Cooper pairs. Importantly, the emergence of phonon-coupling bands is mainly dependent on the ionization of sp3-hybridized σ-bonds within NH3, resulting in the manifestation of metallicity. Due to the enhanced ionization of σ-bands and strengthened interatomic coupling effect with pressurization, the Tc is further enhanced to 130 K. Our study offers novel insights towards the realization of phonon-mediated high-temperature superconductivity at comparatively low-pressures and highlights the potential for achieving high-Tc in filled f-shell metal hydrides through strategic engineering of metallized σ-bonds.