Study of Single Electron Charging Effects

The program Study of Single Electron Charging Effects^, supported by Grant-in-Aid for Specially Promoted Research from the Ministry of Education, Science and Culture (1993-1995) has been successfully concluded. Among the 14 themes scheduled at the begining, 8 have been accomplished and the rests are still going on. The followings are the major results. 1. It was shown that the Coulomb blockade in normal small tunnel junctions appears when the tunnel resistance is larger than the universal value, h/e^*2. 2. It was shown that even with the condition above, the blockade disappears when the impedance between the array and the environment is smaller than h/e^*2. 3. It was shown that for a finite Josephson current in small superconducting junctions, the tunnel resistance should be smaller than h/4e^*2. 4. In 2-dimensional arrays of high-resistive junctions, a precursor of the charge Kosterlitz-Thouless transition was observed. 5. In superconducting 2-dimensional arrays, the superconductor-insulator transitions were observed, and the phase boundaries were determined. 6. Using above results, a phase diagram in a temperature-tunnel resistance-charging energy space was determined. It agreed well with a theoretical prediction. 7. To examine the effect of randomness, similar experiments as 4,5 and 6 were performed with the samples that consisted of rendomly packed small metal particles. No essential difference was observed.