Cooper-pair resonances and subgap Coulomb blockade in a superconducting single-electron transistor

TL;DR

This paper reports on the fabrication and measurement of superconducting single-electron transistors with Al leads and Nb islands, revealing Cooper-pair resonances and Coulomb blockade effects at subgap voltages, supported by numerical simulations.

Contribution

It demonstrates the observation of Cooper-pair resonances and Coulomb blockade in a novel superconducting transistor configuration with experimental and simulated validation.

Findings

Clear signatures of resonant tunneling of Cooper pairs

Coulomb blockade of subgap currents observed

Good agreement between experiments and simulations

Abstract

We have fabricated and measured superconducting single-electron transistors with Al leads and Nb islands. At bias voltages below the gap of Nb we observe clear signatures of resonant tunneling of Cooper pairs, and of Coulomb blockade of the subgap currents due to linewidth broadening of the energy levels in the superconducting density of states of Nb. The experimental results are in good agreement with numerical simulations.