Superconductivity of CeRu2

Ever since Matthias pointed out the possibility of the coexistence of magnetism and superconductivity in the Laves phase (C15) compound CeRu2 (superconductor with Tc≅6.1 K) with magnetic rare earth substitution at the Ce site, it has remained a subject of attention. So far, it has been traditionally assumed that Ce in CeRu2 is tetravalent, i.e., 4f0, but X-ray photoemission spectroscopy (XPS) as well as resonant photoemission and X-ray absorption studies strongly indicate that the f-electron count approaches one in this compound. This later picture has received strong support from the theoretical front. This new status of CeRu2 demands reexamination of the nature of its superconductivity. Here we would like to present the results of our ac susceptibility and resistivity measurements on (Ce1-xTx)Ru2, where T=La, Nd, Lu, Th and U and to interpret these results in the light of recent theoretical developments. (orig.)