The Cooper-pair tunneling in superconducting charge boxes in tunable electromagnetic environments is experimentally studied using a single-electron-transistor electrometer and via current-voltage characteristics measurement with small excitations. In the low-impedance regime, the environmental effect is quantified with an effective Josephson coupling energy, which is found to decrease as the environment impedance increases. In the high-impedance regime, the Cooper-pair tunneling is blockaded. For impedance above $250\phantom{\rule{0.3em}{0ex}}\mathrm{M}\ensuremath{\Omega}$, Coulomb oscillation of the zero-bias conductance suggests that Cooper-pair tunneling is completely suppressed and subgap quasiparticle tunneling becomes dominant.The Cooper-pair tunneling in superconducting charge boxes in tunable electromagnetic environments is experimentally studied using a single-electron-transistor electrometer and via current-voltage characteristics measurement with small excitations. In the low-impedance regime, the environmental effect is quantified with an effective Josephson coupling energy, which is found to decrease as the environment impedance increases. In the high-impedance regime, the Cooper-pair tunneling is blockaded. For impedance above $250\phantom{\rule{0.3em}{0ex}}\mathrm{M}\ensuremath{\Omega}$, Coulomb oscillation of the zero-bias conductance suggests that Cooper-pair tunneling is completely suppressed and subgap quasiparticle tunneling becomes dominant.

Physical Review BJan 11, 20072 citations

2etoeperiodic pair currents in superconducting Coulomb-blockade electrometers

A. Amar, D. Song, Christopher J. Lobb +1 more

We have measured the current as a function of gate charge Q in superconducting Coulomb blockade electrometers with charging energies ${\mathit{E}}_{\mathit{c}}$ \ensuremath{\ll}\ensuremath{\Delta}, the superconducting gap. We find a large pair current which exhibits a clear transition from 2e to e periodicity at about 250 mK. To explain our data, we propose an equilibrium model in which the current is due entirely to Cooper pairs. The periodicity change results from rapid shifts in the instantaneous effective Q, caused by fluctuations in quasiparticle number. We find good agreement, and predict the loss of 2e periodic current for large ${\mathit{E}}_{\mathit{c}}$ .We have measured the current as a function of gate charge Q in superconducting Coulomb blockade electrometers with charging energies ${\mathit{E}}_{\mathit{c}}$\ensuremath{\ll}\ensuremath{\Delta}, the superconducting gap. We find a large pair current which exhibits a clear transition from 2e to e periodicity at about 250 mK. To explain our data, we propose an equilibrium model in which the current is due entirely to Cooper pairs. The periodicity change results from rapid shifts in the instantaneous effective Q, caused by fluctuations in quasiparticle number. We find good agreement, and predict the loss of 2e periodic current for large ${\mathit{E}}_{\mathit{c}}$.

Physical Review LettersMay 16, 199464 citations

We have measured the current as a function of gate charge Q in superconducting Coulomb blockade electrometers with charging energies

{\mathit{E}}_{\mathit{c}}

\ensuremath{\ll}\ensuremath{\Delta}, the superconducting gap. We find a large pair current which exhibits a clear transition from 2e to e periodicity at about 250 mK. To explain our data, we propose an equilibrium model in which the current is due entirely to Cooper pairs. The periodicity change results from rapid shifts in the instantaneous effective Q, caused by fluctuations in quasiparticle number. We find good agreement, and predict the loss of 2e periodic current for large

{\mathit{E}}_{\mathit{c}}