Effects of quantum levels on transport through a Coulomb island

Transport measurements are used to study the quantized energy levels in a small electron gas, referred to as a Coulomb island. First, large-bias measurements reveal the excitation spectrum of the island. Second, small-bias measurements probe the intrinsic line shape of energy levels. Line shapes are generally fit well by thermally broadened Lorentzians. In addition, a decrease in the charging energy of the island is observed as the coupling to its leads is increased. This effect is shown to be consistent with a dramatic increase in one of the island-lead capacitances.