( M= Fe, Co, Ni): Ab initio study on electron-phonon coupling, rattling modes, and anharmonic effects.

In recent experiments by Y. Shinoda et al., J. Phys. Soc. Japan 92, 103701 (2023), the superconductivity of a new family of materials, Sc₆MTe₂ (M= 3d, 4d, 5d elements), has been observed. In this study, we employ density functional perturbation theory and self-consistent phonon theory to investigate the role of electron-phonon coupling in Sc₆MTe₂ (M= Fe, Co, Ni). Our predicted transition temperatures, importantly, reproduce the chemical trend. We attribute superconductivity to the electronegativity difference between Sc and the M element, which suppresses the magnetism of Fe, Co, and Ni, possibly influencing the spin fluctuations in Sc, avoiding the suppression of the superconductivity. In the M = Fe and Co cases, we observe rattling phonon modes contributing to strong electron-phonon coupling. We also find imaginary modes for M = Fe due to anharmonicity. Interestingly, renormalized phonon bands yield a significant plateau in the Eliashberg spectral function, enhancing superconductivity. Our findings propose a novel material design strategy for phonon-mediated superconductors with d-elements, combining non-superconducting and magnetic elements. This study also underscores the role of rattling modes and anharmonicity in electron-phonon interactions and, consequently, superconductivity.