Contrasting fate of holes introduced by Fe or In in kagome metal CoSn

Abstract

CoSn is a kagome metal with well-defined flat bands 0.2 eV below the Fermi level EF. Moving them across EF would offer a rare opportunity to investigate their impact on electronic properties. Using angle-resolved photoemission spectroscopy (ARPES) and X-ray absorption at the Co K-edge, we examine two routes to introduce holes in this compound, through Co/Fe or Sn/In substitutions. Substituting In for Sn produces an almost rigid upward shift of the bands toward EF, as expected for hole doping, whereas substituting Fe for Co leads to an unexpected downward shift. Density functional theory calculations reproduce these opposite trends and trace the unusual behavior of Fe to its local magnetic moment. The moment keeps the hole on the Fe impurity and imposes an attractive electrostatic potential on neighboring Co atoms. Overall, both substitutions bring weakly dispersing states close to EF, the flat bands of the Co kagome lattice upon In substitution and partly localized states around magnetic Fe impurities upon Fe substitution.