Disorder and Interaction-Induced Pairing in the Addition Spectra of Quantum Dots

We have numerically investigated the electron addition spectra in quantum dots containing a small number $\left(N\le 10\right)$ of interacting electrons, in the presence of strong disorder. For a short-range Coulomb repulsion, we find regimes in which two successive electrons enter the dot sequentially but almost at the same value of the chemical potential. In the strongly correlated regime these close additions, or pairings, are associated with electrons tunneling into distinct electron puddles within the dot. We discuss the tunneling rates at pairing and argue that the results are related to a recently observed phenomenon known as bunching.