Coulomb-blockade oscillations in a quantum dot strongly coupled to leads

We report on the behavior of Coulomb-blockade oscillations in a semiconductor quantum dot, when its coupling to the leads is strong, i.e., of the order of the dot’s energy-level separation. Under magnetic fields 0.75≤B≤4 T, we find a periodic amplitude modulation of both the peaks and the valleys of the conductance resonances. Assuming that only the lowest edge channel carries current, we apply a model, describing partly coherent and partly incoherent electron transport, to explain these modulations. Within this model, the period of the amplitude modulation reflects the filling factor inside the dot. The amplitude of the envelope function is determined by the fraction of electrons scattered inelastically in the dot, the electron temperature, and the transmission of the tunnel barriers that couple the dot to the reservoirs. We show that it is only in the strong coupling regime where we can distinguish between thermal broadening and broadening as a consequence of inelastic scattering. We use this model to estimate the electron temperature as well as the phase-coherence length inside the quantum dot. The modulation of the conductance valleys is related to a periodic modulation of cotunneling rates.