Pumping characteristics were studied of a hybrid normal-metal/superconductor single-electron transistor embedded in high-Ohmic environment. Two 3 μm long microstrip resistors of CrOx with a sum resistance R≈80 kΩ were placed adjacent to the transistor. Substantial improvement of pumping and a reduction of the subgap leakage were observed in the low-megahertz range. At higher frequencies (0.1–1 GHz), pumping performance deteriorated compared to reference devices without resistors by the slowdown of tunneling and by electronic heating.
Lotkhov, S. V., Kemppinen, A., Kafanov, S., Pekola, J. P., & Zorin, A. B. (2009). Pumping properties of the hybrid single-electron transistor in dissipative environment. Applied Physics Letters, 95(11). https://doi.org/10.1063/1.3227839