COTUNNELING AND RENORMALIZATION EFFECTS FOR THE SINGLE-ELECTRON TRANSISTOR

We consider transport properties through a small metallic island in th e perturbative regime. For this purpose we present a diagrammatic expa nsion of the reduced density matrix up to fourth order in the tunnelin g matrix elements (cotunneling). Improving our previous theory, we are able to calculate the occupation of the island as well as the conduct ance through tie transistor at arbitrary temperature and bias voltage. Furthermore, we determine the renormalization of the system parameter s and extract the arguments of the leading logarithmic terms (which ca nnot be derived from usual renormalization-group analysis). We perform the low- and high-temperature limits. In the former, we find a behavi or characteristic for the multichannel Kondo model. We find quantitati ve agreement with recent experiments. [S0163-1829(98)08636-6].