Addition spectra in disordered quantum dots with strongly interacting electrons

We report on numerical simulations of the electron addition spectra in quan tum dots weakly coupled to one charge reservoir, and containing a small num ber (N less than or equal to 10) of particles. In particular, we investigat e the role played by disorder and electron-electron interaction in creating a surprising feature, known as "electron bunching", recently observed expe rimentally. In dots where disorder and on-site repulsion are both strong, a nd the direct Coulomb repulsion is short range, we find examples of two ele ctrons entering the dot at very close values of the gate voltage. Whenever such pairing occurs, the first electron involved in the pair appears at the edge of the quantum dot. Furthermore, the tunneling rate of the second ele ctron is much faster than that of the first. We also find that the total sp in of the many-body ground state is partially polarized after the second el ectron enters the dot. The dependence of the addition spectrum as a functio n of the magnetic field is discussed.