EVEN-ODD ELECTRON NUMBER EFFECTS IN SMALL SUPERCONDUCTING ISLANDS

We present experiments in which the even-odd electron number dependenc e of a superconducting island is investigated by way of electron tunne ling. The experiments are performed in a single-electron transistor co nfiguration in which a superconducting Al island is in tunneling conta ct with either superconducting Al or normal Au bias electrodes. A gate electrode is used to modify the island charge. A salient 2e periodic behavior appears in the tunneling current versus gate charge character istic as a result of an even-odd free energy difference F(o). The expe rimental 2e to e periodicity crossover line T (H) is in excellent agr eement with theoretical predictions. With normal leads the current is attributed to an Andreev-like tunneling process which depends on the p arity of the number of electrons on the island.