Fine structure in the off-resonance conductance of small Coulomb-blockade systems

We show how a fine, multiple-peak structure can arise in the off-resonance, zero-bias conductance of Coulomb-blockade systems. In order to understand how this effect comes about one must abandon the orthodox, mean-field understanding of the Coulomb-blockade phenomenon and consider quantum fluctuations in the occupation of the single-particle electronic levels. We illustrate such an effect with a spinless Anderson-like model for multilevel systems and an equation-of-motion method for calculating Green's functions that combines two simple decoupling schemes.