INFLUENCE OF ELECTROMAGNETIC FLUCTUATIONS ON THE RESONANT-TUNNELING OF ELECTRONS

We have considered the influence of electromagnetic fluctuations on el ectron tunneling via one non-degenerate resonant level, the problem th at is relevant for electron transport through quantum dots in the Coul omb blockade regime. We show that the overall effect of the fluctuatio ns depends on whether the electron bands in external electrodes are em pty or filled. In the empty band case, depending on the relation betwe en the tunneling rate Gamma and characteristic frequency Omega of the fluctuations, the field either simply shifts the conductance peak (for rapid tunneling, Gamma much greater than Omega) or broadens it (for G amma much less than Omega). In the latter case, the system can be in t hree different regimes for different values of the coupling g between electrons and the field. Increasing interaction strength in the region g < 1 leads to gradual suppression of the conductance peak at the bar e energy of the resonant level epsilon(0), while at g much greater tha n 1 it leads to the formation of a new peak of width E(c)/g(1/2) at th e energy epsilon(0) + E(c), where E(c) is a charging energy. For inter mediate values of g the conductance is non-vanishing in the entire ene rgy range from epsilon(0) to epsilon(0) + E(c). For filled bands the p roblem is essentially multi-electron in character. One consequence of this is that, in contrast to the situation with the empty band, the fl uctuations of the resonant level do not suppress conductance at resona nce for g < 1. At g > 1 a Coulomb gap appears in the position of the r esonant level as a function of its bare energy which leads to suppress ion of conductance.