No abstract

Electron transport through parallel double quantum dot system with interdot tunneling and strong on-site Coulomb interaction is studied in the Kondo regime by using the finite-U slave boson technique. For a system of quantum dots with degenerate energy levels, the linear conductance reaches the unitary limit (2e 2 /h) due to the Kondo effect at low temperature when the interdot tunneling is absent. As the interdot tunneling amplitude increases, the conductance decreases in the singly occupied regime and a conductance plateau structure appears. In the crossover to the doubly occupied regime, the conductance increases to reach the maximum value of G = 2e 2 /h.

By decorating single-layer graphene with disordered noble metal (Ag, Au, and Pt) clusters, we investigated experimentally the influence of strong random scatterings on graphene transport and electron-localization phenomena. As evidenced by micro-Raman scattering, there is a strong interction between the metal clusters and graphene. We found that such a strong interaction was the consequence of plasma-assisted decoration of the graphene by the metal clusters. A large negative magnetoresistance (MR) effect (up to 80% at 12 T) was observed and fitted using different models. The structure, size, and area density of metal clusters were characterized by scanning tunneling microscopy and transmission electron microscopy. The samples with a high concentration of scattering centers behaved as insulators at low temperatures and showed strong localization (SL) effects. Their temperature-dependent conductance was in accordance with the two-dimensional variable-range hopping (VRH) mechanism. The localization lengths and density of states were estimated and discussed.

We investigate the full counting statistics of a single quantum dot strongly coupled to a local phonon and weakly tunnel-connected to two metallic electrodes. By employing the generalized nonequilibrium Green function method and the Lang-Firsov transformation, we derive an explicit analytical formula for the cumulant generating function, which makes one to be able to identify distinctly the elastic and inelastic contributions to the current and zero-frequency shot noise. We find that at zero temperature, the inelastic effect causes upward steps in the current and downward jumps in the noise at the bias voltages corresponding to the opening of the inelastic channels, which are ascribed to the vibration-induced complex dependences of electronic self-energies on the energy and bias voltage. More interestingly, the Fano factor exhibits oscillatory behavior with increasing bias voltage and its minimum value is observed to be smaller than one half.