Disorder-Sensitive Superconductivity and Bonding Network in the Iron-Silicide Superconductor Lu2Fe3Si5

We performed experimentally the electron-density mapping on the crystal structure of the iron-based superconductor Lu2Fe3Si5 which revealed the Fe-Si covalent-bonding network with the fully ionized Lu-sites. And, for Lu2Fe3Si5, we investigated the effect of Fe- and Si-site substitutions on the superconductivity. The Fe-site-substitution study revealed that, in addition to the disorder-sensitive superconductivity, the additionally-provided 3d electrons or holes tend to be itinerant rather than localized. Taking into account that the localized magnetic moments introduced on the Lu-sites are inactive as magnetic pair breakers, the present results suggest that, in Lu2Fe3Si5, the Fe-Si bonding network should be the playground for the exotic superconductivity which is characterized by the sign-reversed superconducting gap function.