Mesoscopic noise and admittance of an electrically driven nano-structure

We calculate current noise and admittance of an electrically driven nano-structure in a mesoscopic capacitor plate within Floquet scattering theory. We show that the interplay between quantum statistics and coherence of electrons is important in the photo-assisted non-equilibrium noise. Current noise has two different contributions; photo-assisted non-equilibrium noise and Nyquist equilibrium noise. At low frequencies ω and temperature, the photo-assisted non-equilibrium noise dominates the Nyquist equilibrium noise as their leading terms are proportional to ω2 and ω3, respectively. The Nyquist noise has peak structure as a function of the Fermi energy caused by the large delay time associated with the (photo-assisted) resonant levels. Meanwhile, the photo-assisted current noise is not simply given by the phase delay time at the Fermi level. This is because, unlike the equilibrium noise, the photo-assisted current noise is also contributed from electron states far below the Fermi level. We interpret the real admittance g′(ω) in terms of the photo-assisted phase delay time.