Abstract
A superconducting Coulomb-blockade electrometer was used to measure the Coulomb staircase of an Cooper-pair box from a temperature of . At the lowest temperature, the Coulomb staircase displays effects from nonequilibrium quasiparticles. As the temperature is increased, an initial decrease is found in the width of the odd steps in the staircase, which corresponds to a reduction in the probability of having a quasiparticle on the island of the box. Above , the width of the odd steps increases, eventually producing a staircase with features. We develop a steady-state model of the system and find that the presence of quasiparticles at low temperature is consistent with the assumption of Aumentado et al. [Phys. Rev. Lett. 92, 066802 (2004)] that nonequilibrium quasiparticles are generated in the leads. Above , our results are consistent with the quasiparticle states of the island being thermally populated.
- Received 19 January 2007
DOI:https://doi.org/10.1103/PhysRevB.76.054501
©2007 American Physical Society