Signature of f -electron conductance in α -Ce single-atom contacts

Cerium is a fascinating element exhibiting, with its different phases, long-range magnetic order and superconductivity in bulk form. The coupling of the 4f electron to sd conduction electrons and to the lattice is responsible for unique structural and electronic properties like the isostructural first-order solid-solid transition from the cubic γ phase to the cubic α phase, which is accompanied by a huge volume collapse of 14%. We report experiments aiming at disentangling the 4f contribution to the electric conductance of the different phases. On single-atom Ce contacts we observe a strongly enhanced conductance G. By controlling the content of α-Ce employing different rates of cooling, we find a strong correlation between the fraction of α-Ce and the magnitude of G at the last conductance plateau before the contact breaks. We attribute the enhanced conductance of α-Ce to the additional contribution of the 4f level.