Parity effect in a superconducting single-electron transistor with a 20-nm island

With a, specially-designed three-angle shadow evaporation, we fabricated an Al-based single-electron transistor with a 20-nm island. We investigated electron transport through the single-electron transistor in the superconducting state as a function of the source-drain voltage as well as the gate voltage. 2e-periodic small current plateaus appeared. We attribute the origin of this structure to the odd number states of electrons in the island. Compared with a theoretical calculation, it showed a reasonable agreement at low temperatures and low source-drain voltages, while at higher voltages the parity effect diminished.