Kondo-assisted and resonant tunneling via a single charge trap: A realization of the Anderson model out of equilibrium

We have observed both Kondo-assisted tunneling and simple resonant tunneling via a single charge trap state in the voltage-dependent differential conductance of a point-contact tunnel barrier. From the resonant tunneling signal, we determine parameters of the Anderson model governing the state. This allows comparison of the measured Kondo-assisted signal to results of the Anderson model. The Kondo signal is not adequately described by perturbation theory, but is in qualitative agreement with nonperturbative calculations.