Magnetic-field-induced crossover from 2e to e periodicity in the superconducting single-electron transistor.

Abstract

We present extensive experimental data on the gate-charge-periodic current I(${\mathit{Q}}_{\mathit{o}}$) through a single-electron transistor as a function of the applied magnetic field. This device consists of a mesoscopic superconducting island which is coupled to two macroscopic superconducting leads through small tunnel junctions and to a capacitive gate. The behavior of the system exhibits two separate transitions as the magnetic field is increased. In the first, the I-${\mathit{Q}}_{\mathit{o}}$ curves cross from 2e to e periodicity in ${\mathit{Q}}_{\mathit{o}}$ while two-electron tunneling is still the dominant charge transport mechanism. In a second transition that occurs at higher magnetic fields, single-electron tunneling becomes the dominant mechanism. This transition from two-electron to single-electron tunneling shifts the maxima of the I-${\mathit{Q}}_{\mathit{o}}$ curves by e/2 in ${\mathit{Q}}_{\mathit{o}}$, and results in a significant increase in the current magnitude. Both transitions can be understood by considering how superconductivity in the leads and the island is affected by an increasing magnetic field. \textcopyright{} 1996 The American Physical Society.