CROSSOVER FROM SINGLE-LEVEL TO MULTILEVEL TRANSPORT IN ARTIFICIAL ATOMS

Measurements are reported of the temperature dependence of the conduct ance through a small region of electron gas separated from its leads b y tunnel junctions. The quantization of charge and energy in the small region gives rise to sharp, nearly periodic peaks in the conductance as a function of electron density, one for each electron added to the isolated region. Because the charge and energy are quantized, we call this an artificial atom. At low temperature, the conductance is limite d by resonant tunneling through a single quantum level of the artifici al atom,; but at high temperatures several levels participate. Changes in the temperature dependence of the width and height of conductance peaks display clear evidence for this crossover from single-level to m ultilevel transport.