EFFECTS OF MACROSCOPIC QUANTUM TUNNELING OF CHARGE IN ULTRASMALL SET DOUBLE-JUNCTIONS WITH EXTERNAL ELECTROMAGNETIC ENVIRONMENT

It is known that classical Coulomb blockade effects of SET devices are disturbed by the tunneling effects of higher order denoted as macroscopic quantum tunneling of charge (q-mqt) or co-tunneling. The influence of an external electromagnetic environment modelled by an additional impedance in the circuit on the mean q-mqt current is studied in the high-impedance limit. This is important especially for devices containing only two SET junctions, for instance the SET electrometer, where the influence of the environment on the Coulomb blockade is remarkable. It can be shown that the Coulomb blockade is only partly destroyed producing a new, lower “quantum” Coulomb blockade. This holds as well in the case of the incoherent as of the coherent q-mqt. Furthermore, a method is presented on how to regularize the logarithmic singularities in the q-mqt current using line width effects.