Strong Tunneling in the Single-Electron Transistor

We have investigated the suppression of single-electron charging effects in metallic single-electron transistors when the conductance of the tunnel junctions becomes larger than the conductance quantum ${e}^{2}/h$. We find that the Coulomb blockade of the conductance is progressively shifted at lower temperatures. The experimental results agree quantitatively with the available $1/T$ expansion at high temperature, and qualitatively with the predictions of an effective two-state model at low temperature, which predicts at $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ a blockade of conductance for all gate voltages.