The applications of nonlinear dynamic admittance in nanostructures

Motivated by applications of second-order nonlinear capacitances in semicon ductor measurements of charge carrier densities, we investigate the profoun d relationship between the second-order nonlinear emittance and the total a nd partial local densities of states for tunnelling transport in nanoscale systems with ac bias. We have derived an explicit formula for the second-or der nonlinear emittance in the case of low frequencies. The difference betw een the emittance and capacitance in actual measurements is elaborated; and we show that the total density of states completely determine the second-o rder nonlinear emittance. Our study indicates that the second-order nonline ar emittance equals the second-order nonlinear electrochemical capacitance when there is no tunnelling current and the density of states is macroscopi c. Also, in the quantum regime, the second-order emittance does not vanish even if the pure geometric capacitance equals zero. Based on our results, w e present an application of the second-order nonlinear emittance in nanosca le systems.