We observed current-voltage characteristics of superconducting single charge transistors with on-chip resistors of R about R_Q = h/4e^2 = 6.45 kOhm, which are explained in terms of Cooper-pair cotunneling. Both the effective strength of Josephson coupling and the cotunneling current are modulated by the gate-induced charge on the transistor island. For increasing values of the resistance R we found the Cooper pair current at small transport voltages to be dramatically suppressed.
@article{arxiv.cond-mat/0305113,
title = {Cooper pair cotunneling in single charge transistors with dissipative electromagnetic environment},
author = {S. V. Lotkhov and S. A. Bogoslovsky and A. B. Zorin and J. Niemeyer},
journal= {arXiv preprint arXiv:cond-mat/0305113},
year = {2009}
}