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 propose a simple phenomenological expression for the resulting Fano interference that 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 life-time of the heavy quasiparticle excitations that agrees well with recent state-of-the-art numerical calculations.
Categories: cond-mat.str-el