Differential conductance and quantum interference in kondo systems

We present a large-N theory for the differential conductance, dI=dV, in Kondo systems measured via scanning tunneling spectroscopy. We demonstrate that quantum interference between tunneling processes into the conduction band and into the magnetic f-electron states is crucial in determining the experimental Fano line shape of dI=dV. This allows one to uniquely extract the Kondo coupling and the ratio of the tunneling amplitudes from the experimental dI=dV curve. Finally, we show that dI=dV directly reflects the strength of the antiferromagnetic interaction in Kondo lattice systems.