RESONANT COOPER-PAIR TUNNELING IN VOLTAGE-BIASED SUPERCONDUCTING SINGLE-ELECTRON TRANSISTORS

We investigate the I-V characteristics of SET transistors where the is land as well as the electrodes are superconducting. Coherent Cooper-pa ir tunneling results in a mixing of the charge eigenstates of the elec trodes. Tunneling of quasiparticles causes transitions between the eig enstates of the system and, thus, produces a de-current. Similarly, th e coupling to a fluctuating electromagnetic environment leads, to diss ipative tunneling of Cooper pairs. The current can be tuned by a gate voltage. Due to parity effects the current becomes 2e-periodic in the gate charge. We evaluate the I-V characteristics in the framework of a model which accounts for these effects. The theoretical results are i n good agreement with recent experiments.