Geometric blockade in a quantum dot:  Transport properties by exact diagonalization

We report exact diagonalization studies of quantum dots in which energetics due to electron-electron interaction, magnetic field, and geometrical factors compete and induce interesting ground-state electron configurations. The geometrical effect is generated by a confining potential in the form of a ring with a quantum dot in the middle. Due to the spatial localization of electrons in the two different potential regions, abrupt electron redistribution occurs as the magnetic field is increased. A new transport blockade is predicted in this system in addition to the familiar Coulomb and spin blockades. We calculate the addition spectra of the dot confining a small number of electrons, and using the exact spectral function, we evaluate the tunneling current by the Keldysh nonequilibrium Green’s function formalism. The geometrically induced blockade drastically diminishes the tunneling current.