Asymmetrical tunneling in heavy fermion metals as a possible probe for their non-Fermi liquid peculiarities

Tunneling conductivity and point contact spectroscopy between heavy fermion metal and a simple metallic point contact may serve as a convenient probing tool for non-Fermi liquid behavior. Landau Fermi liquid theory predicts that the differential conductivity is a symmetric function of voltage bias. This symmetry, in fact, holds if so called particle-hole symmetry is preserved. Here, we show that the situation can be different when one of the two metals is a heavy fermion one whose electronic system is a heavy fermion liquid. When the heavy fermion liquid undergoes fermion condensation quantum phase transition, the particle-hole symmetry in the excitation spectra is violated making both the differential tunneling conductivity and dynamic conductance asymmetric as a function of applied voltage. This asymmetry can be observed when the heavy fermion metal is either normal or superconducting. We discuss also the possible experiments to study the above asymmetry and note that asymmetric conductivity has been recently observed in measurements on CeCoIn5.