On the origin of the conductance asymmetry in CeMIn₅ (M=Co, Rh, Ir)

Asymmetric differential conductance has been frequently observed in heavy fermion point-contact junctions. We report such data obtained from the Ce-based 1-1-5 compounds CeMIn₅ (M=Co, Rh, Ir). Apart from characteristics due to superconductivity or antiferromagnetism, a striking common feature is an asymmetry in the background conductance, which shows nontrivial temperature and voltage dependencies. These behaviors cannot be explained by the local heating model combined with large Seebeck effect in heavy fermions. We propose that a Fano-like interference may cause the asymmetry. The interference can occur between two conductance channels, one into the conduction band and the other into the heavy electron band formed by the hybridization of conduction electrons with localized f-electrons.