ac response of an interacting quantum dot in a nonequilibrium state

We present a investigation about the ac response of the quantum-dot system that is described by the Anderson model and some parasitic capacitances. Under the Anderson model, a general criterion of charge conservation for the time-dependent transport is given by use of the equation of motion for the nonequilibrium Green’s function. To give a qualitative study of ac response at nonequilibrium states, we make a rough approximation for the lesser Green’s function, which satisfies the charge conservation law. Linear response to a harmonic ac bias voltage has been calculated, and both frequency-dependent conductances and phase shifts display the evident characteristic of the double Fermi level at nonequilibrium state. We show that the two Fermi levels can be determined from phase-shift curve $\delta \sim \omega$ and ac conductance curve $G\sim \omega .$ Furthermore, the total ac responses including the capacitive currents, are calculated and still indicate the obvious characteristic of the Kondo effect.