Chemical Bonding Topology of Superconductors

Abstract

Heavy fermion superconductors can be classified into the following two types based on their structures: (1) ternary transition metal carbides, borides, and silicides containingf-block metals exhibiting stable multiple oxidation states such as cerium in CeCu2Si2, CeRu3B2, and CeRu3Si2or uranium in URu2Si2and U2PtC2; (2) binary alloys containing multiple oxidation state actinides (particularly uranium) and nonactinide polyhedral clusters such as Be13centered icosahedra in UBe13and Pt6/2octahedra in UPt3. Thef-block metals in heavy fermion superconductors not only exhibit multiple oxidation states but are also diluted enough by the other elements so that the separation betweenf-block metals in the structure is at least 4 Å. Thef-block metals become part of the conducting skeletons of heavy fermion superconductors so that their conductivities arise at least partially through valence fluctuations involvingf-electrons.