Effect of Fe doping on the electronic properties of CoSn Kagome semimetal

Quantum phenomena in two-dimensional Kagome materials lead to exotic topological states and complex magnetism. Here, we have investigated the detailed electronic properties of Co1-xFe_<i>x</i>Sn as a function of composition (<i>x</i>) to explore the competing electronic interactions for the origin of complex magnetism and topological properties. We find that the screening effect in the valence electrons increases while the correlation effect decreases with an increase in the Fe doping. Valence fluctuations observed at Co and Fe<i>L</i>2,3edges showed systematic changes in the magnitude of divalent and trivalent states with the increase in<i>x</i>. Fe 3<i>d</i>states are found to be more screened by the conduction electrons than the Co 3<i>d</i>states. A comparison of the theoretical and experimental density of states showed different natures of localized states with strong screening effects on the surface and dominating correlation effects in the bulk for<i>x</i>>0. We have observed localized flat bands on the CoSn (001) surface while quasi-localized flat bands on the Co_0.94Fe_0.06Sn (001) surface. The distinct character of the bulk and surface band structure is confirmed in the Fe-doped composition. Hence, the bulk-surface interaction present in Co1-xFe_<i>x</i>Sn gives rise to the origin of valence fluctuation, complex magnetism, and topological properties.