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

Abstract

The conductance and the current of spherical quantum dots ͑SQD's͒ 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 manyparticle states of the SQD's are described by the total spin ͑S͒ and total orbital ͑L͒ angular momenta (LS-coupling scheme͒ 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.In order to obtain the transport properties we will follow the same formalism described in Ref. 2 for one-dimensional systems. We consider a double barrier system formed by two

Quantum dot as thermal rectifier

“…Resonance lines outside the CB diamonds originate from transport through excited states (µ n+1,i;n,j ), where (i, j) ǫ N + [12]. The ap- pearance of areas with negative differential conductance (white areas) is typically a signature of the occurrence of blocking mechanisms of various kinds [13,14]. Especially for B = 0, the SET resonance µ (N +2;N +1) exhibits a negative differential conductance for V DS < 0 V and V P < −2.21 V [onset indicated by an arrow Fig.…”

The violation of the Hund rule in semiconductor artificial atoms

“…At last, in order to prove the efficiency of the Pople-Nesbet approach, we compared the results from this UHF self-consistent matrix formulation with the ones obtained from the LS-coupling scheme used in Ref. [28], where a GaAs QD having R 0 = 90 Å was considered, and the quadratic term in B 0 was neglected since only small fields were considered; also, only N = 2 and N = 3 occupations were calculated, since the states were exactly built (not only a single Slater determinant), and the electronelectron interaction was included by using perturbation theory, justified at such radius. At zero field the energies for N = 2 are 16.5 meV (LS) and 16.1 meV (UHF), while for N = 3 they are 34.8 meV (LS) and 33.9 meV (UHF); so, the formalism here used indeed give smaller ground state energies than the LS perturbation scheme.…”

Restricted and unrestricted Hartree–Fock approaches applied to spherical quantum dots in a magnetic field

“…At last, we have compared the results from both RHF and UHF self-consistent matrix formulations with the ones obtained from the LS-coupling scheme used in Ref. [35], where a GaAs QD having R 0 = 90 Å was considered, and the quadratic term in B 0 was neglected since only small magnetic fields were considered. Also, only N = 2 and N = 3 occupations were calculated, since the states were constructed analytically (not only a single Slater determinant), and the electron-electron interaction was included by using perturbation theory, that is justified at such radius.…”