Measurement of the superconducting single electron transistor in a high impedance environment

Abstract

We have fabricated and measured a capacitively coupled, superconducting, single electron transistor (S-SET) with special high resistance biasing leads. The leads provided a source of charge for the S-SET, with an impedance at high frequencies which was greater than the quantum resistance R Q = h/4e 2 = 6.45 kΩ . The current-voltage characteristic of the S-SET biased in this way, showed a Coulomb blockade of Cooper pair tunneling. We have studied the modulation of this blockade with the gate voltage, measured at fixed DC current. The period of modulation in gate voltage was 2 e/ C g, where C g is the gate capacitance. We describe the dependence of this voltage modulation, and the crossover from 2 e periodic to e periodic behavior, as a function of temperature, DC measurement current, and externally applied perpendicular magnetic field. The results obtained are compared with other experimental data on the S-SET in a low impedance environment where an explanation based on the parity model exists.