Parity Effects in Single Charge Tunneling
The subject of this thesis is single charge tunneling effects, especially parity effects, as they are manifested in quantum mechanical tunneling through a metallic island small enough to cause single electrons to block tunneling of other electrons due to Coulomb interaction. When the island is superconducting the ground state energy depends on the parity of the number of electrons on the island: outside of the condensate there will always be at least one electron contributing to the energy for an odd number of electrons and this will have observable consequences.
In papers I and II a configuration with Cooper pair tunneling through an island between superconductors is studied. We show the emergence of a threshold behaviour at the point where the superconducting gap and the Coulomb energy are equal in size, as well as a change in the modulation of critical current by an external potential. These effects are results of parity change. The current from ballistic tunneling through a normally conducting metallic island is shown to be exponentially decaying with temperature. This is a manifestation of the mesoscopic nature of this kind of transport.
Papers III, IV, and V all deal with a superconducting grain with normally conducting leads. The shot noise in the system is calculated in papers III and IV and we show that it is parity dependent. Noise measurements are suggested as a supplement to the study of I-V characteristics.
Photon assisted tunneling is studied in paper V. We predict a parity change of the grain due to AC modulation of transport and gate bias. The effect should be steps in the peak in the I-V characteristics resulting from Andreev tunneling as well as a decrease and displacement of the peak maximum.
single charge tunneling