ac Response in the Nonequilibrium Anderson Impurity Model

The ac response of a single Anderson impurity coupled to two reservoirs with different chemical potentials is studied using an equation of motion approach. In the Kondo regime, we show that resonant behavior in the ac response is found in the low-frequency limit and the frequency of the ac field matches the chemical potential differences. The resonant behavior is a direct consequence of the ``double'' Kondo peak structure in the one-electron spectral function.