Effective charging energy and conductance of ultrasmall tunnel junctions coupled to an external electromagnetic environment

Tunneling processes in ultrasmall tunnel junctions surrounded by an electro magnetic environment have been investigated with a nonperturbative approach . The derived functional integral representation of the transport current a s a function of the junction voltage clearly indicates that the effective c harging energy and the effective external conductance depend on the junctio n conductance. Via these effective parameters, we can map the nonperturbati ve formula of the action onto the perturbative one. Consequently, the tunne ling current can be calculated for the first time beyond the perturbation t heory. Our theory provides a better understanding of the measured current-v oltage characteristics. (C) 1998 Elsevier Science Ltd. All rights reserved.