Aluminum single-electron transistors studied at 0.3 K in different transport regimes

We measured the transport properties and charge noise of superconducting si ngle-electron transistors at the temperature of 0.3 K. The devices were fab ricated with different ratios between charging and Josephson energies in or der to explore their behavior in different experimental situations. We show that, in spite of the substantial thermal fluctuation, it is possible to e xtract from the data the values of the device parameters and information on the various tunneling mechanisms. Furthermore, we measured the device nois e at different bias points, corresponding to regions with different dominan t tunneling mechanisms, namely in the supercurrent, in the Josephson quasip article, and in the sequential tunneling regions. (C) 2001 American Institu te of Physics.