Coulomb blockade spectroscopy of tunnel-coupled quantum dots

This thesis presents experimental studies of interactions in systems of coupled quantum dots. Quantum dots are often referred to as "artificial atoms" because the number of electrons on a dot is quantized, and those electrons occupy quantized energy levels. Two quantum dots coupled together by interdot electron tunneling may be considered an "artificial molecule". In this thesis we study artificial molecules composed of two quantum dots connected in series and use Coulomb blockade spectroscopy to measure the analog of a molecular binding energy. These measurements reveal how the effects of charge quantization on each individual dot are destroyed as interdot electron tunneling increases in both zero and strong magnetic fields.; In one set of experiments, we use transport measurements to monitor the double dot charge configuration as interdot electron tunneling is increased from near zero, where the dots are almost completely separated, to strong tunneling, where they are entirely joined by quantum mechanical charge sharing. These measurements demonstrate that in zero magnetic field, charge quantization effects on the two individual dots are destroyed when the interdot tunnel conductance is exactly 2e{dollar}sp2{dollar}/h. The charging diagram is shown to evolve in quantitative agreement with recent many body theories.; In other experiments, we study double quantum dots in the quantum Hall regime by applying a strong perpendicular magnetic field to the sample. We find that charge quantization weakens as the quantum Hall edge states on the two dots join, with quantization effects completely destroyed at e{dollar}sp2{dollar}/h of interdot tunnel conductance. Finally, we find that as the magnetic field is varied, the electron distribution readjusts to minimize the energy. The adjustments form a pattern that repeats with magnetic field and with the addition of electrons.