Transport properties in spherical quantum dots: Orbital-blockade and spin-blockade effects

The conductance and the current of spherical quantum dots (SQD’s) containing a small number of electrons are studied as a function of source-drain and gate voltages. The influences of magnetic field, spatial symmetry, electron-phonon interaction, dot radius, and temperature on the transport properties are analyzed. The many-particle states of the SQD’s are described by the total spin (S) and total orbital (L) angular momenta $(LS-\mathrm{coupling}$ scheme) within the Hartree-Fock approximation, where the electron-electron interaction is included via a multipole expansion. The tunneling current is obtained by solving the master equation for the occupation number of the many-particle states of the system. The appearance of a negative differential conductance, due to the orbital-blockade mechanism directly related to the spherical central potential of the quantum dot, is reported.