Conductance asymmetry in point-contact junctions on the heavy-fermion compounds CeMIn$_{5}$ (M=Co, Rh, Ir)

The Ce-based 1-1-5 heavy-fermion compounds, CeMIn$_{5}$ (M=Co, Rh, Ir), continue to draw much attention from the community. One of the key questions is how the localized discrete states acquire itinerancy over the conduction electron continuum. As a probe of the evolutionary behavior of the Kondo lattice, we take differential conductance spectra from nanoscale metallic junctions on CeMIn$_{5}$ single crystals over wide temperature ranges. A striking common feature is the systematic development of an asymmetry in the background conductance [1]. Conventional models including the heating model with large Seebeck coefficients of heavy fermions do not account for this behavior. We propose a phenomenological model based on a possible Fano interference effect [2] between two conductance channels, one into the heavy electron liquid (hybridized f-band) and the other into the conduction electrons without hybridization. [1] W. K. Park et al., Phys. Rev. Lett. \textbf{100}, 177001 (2008). [2] U. Fano, Phys. Rev. \textbf{124}, 1866 (1961).