Fano effect in the point contact spectroscopy of heavy-electron materials

We show that Fano interference explains how point contact spectroscopy in heavy-electron materials probes the emergence of the Kondo heavy-electron liquid below the same characteristic temperature T(*) as that seen in many other experiments and why the resulting measured conductance asymmetry reflects the universal Kondo liquid behavior seen in these. Its physical origin is the opening of a new channel for electron tunneling beyond that available from the background conduction electrons. We derive the Fano formula with a mean-field slave boson approach for the Kondo lattice model and generalize it to finite temperature and realistic situation by introducing empirical parameters. The resulting simple expression for the Fano interference provides a good fit to the experimental results for CeCoIn(5), CeRhIn(5), and YbAl(3), over the entire range of bias voltages, and deduce a lifetime of the heavy quasiparticle excitations that agrees well with recent state-of-the-art numerical calculations.