Anti-Kondo resonance in transport through a quantum wire with a side-coupled quantum dot

An interacting quantum dot side-coupled to a perfect quantum wire is studied. Transport through the quantum wire is investigated by using an exact sum rule and the slave-boson mean field treatment. It is shown that the Kondo effect provides a suppression of the transmission due to the destructive interference of the ballistic channel and the Kondo channel. At finite temperatures, anti-resonance behavior is found as a function of the quantum dot level position, which is interpreted as a crossover from the high temperature Kondo phase to the low temperature charge fluctuation phase.Comment: 4 pages Revtex, 3 eps figure

The Anderson Model out of equilibrium: Time dependent perturbations

The influence of high-frequency fields on quantum transport through a quantum dot is studied in the low-temperature regime. We generalize the non crossing approximation for the infinite-U Anderson model to the time-dependent case. The dc spectral density shows asymmetric Kondo side peaks due to photon-assisted resonant tunneling. As a consequence we predict an electron-photon pump at zero bias which is purely based on the Kondo effect. In contrast to the resonant level model and the time-independent case we observe asymmetric peak amplitudes in the Coulomb oscillations and the differential conductance versus bias voltage shows resonant side peaks with a width much smaller than the tunneling rate. All the effects might be used to clarify the question whether quantum dots indeed show the Kondo effect.Comment: 13 pages, REVTEX 3.0, 5 figure

Finite-temperature Fermi-edge singularity in tunneling studied using random telegraph signals

We show that random telegraph signals in metal-oxide-silicon transistors at millikelvin temperatures provide a powerful means of investigating tunneling between a two-dimensional electron gas and a single defect state. The tunneling rate shows a peak when the defect level lines up with the Fermi energy, in excellent agreement with theory of the Fermi-edge singularity at finite temperature. This theory also indicates that defect levels are the origin of the dissipative two-state systems observed previously in similar devices.Comment: 5 pages, REVTEX, 3 postscript figures included with epsfi

Flicker Noise Induced by Dynamic Impurities in a Quantum Point Contact

We calculate low-frequency noise (LFN) in a quantum point contact (QPC) which is electrostatically defined in a 2D electron gas of a GaAs-AlGaAs heterostructure. The conventional source of LFN in such systems are scattering potentials fluctuating in time acting upon injected electrons. One can discriminate between potentials of different origin -- noise may be caused by the externally applied gate- and source-drain voltages, the motion of defects with internal degrees of freedom close to the channel, electrons hopping between localized states in the doped region, etc. In the present study we propose a model of LFN based upon the assumption that there are many dynamic defects in the surrounding of a QPC. A general expression for the time-dependent current-current correlation function is derived and applied to a QPC with quantized conductance. It is shown that the level of LFN is significantly different at and between the steps in a plot of the conductance vs. gate voltage. On the plateaus, the level of noise is found to be low and strongly model-dependent. At the steps, LFN is much larger and only weakly model-dependent. As long as the system is biased to be at a fixed position relative the conductance step,Comment: 26 revtex APR 94-4

Preemptive CD20+ B cell Depletion Attenuates Cardiac Allograft Vasculopathy in CD154-Treated Monkeys.

BACKGROUND: Anti-CD154 monotherapy is associated with anti-donor alloantibody (Ab) elaboration, cardiac allograft vasculopathy (CAV), and allograft failure in preclinical primate cell and organ transplant models. In the context of calcineurin inhibition (CNI), these pathogenic phenomena are delayed by preemptive “induction” B-cell depletion. METHODS: IDEC-131(αCD154)-treated cynomolgus monkey heart allograft recipients were given peritransplant rituximab (αCD20) alone or with rabbit anti-human thymocyte globulin (rATG). RESULTS: Relative to previously reported reference groups, αCD20 significantly prolonged survival, delayed Ab detection, and attenuated CAV within 3 months in αCD154-treated recipients (αCD154+αCD20 graft median survival time (MST) >90d, n=7, vs 28d for αCD154 alone (IDEC-131), n=21; p=0.05). Addition of rATG to αCD154 (n=6) or αCD154+αCD20 (n=10) improved graft protection from graft rejection and failure during treatment, but was associated with significant morbidity in 8 of 16 recipients (6 infections, 2 drug-related complications). In αCD20-treated animals, detection of anti-donor Ab and relatively severe CAV were anticipated by appearance of CD20(+) cells (>1% of lymphocytes) in peripheral blood, and were associated with low αCD154 trough levels (below 100 µg/ml). CONCLUSIONS: These observations support the hypothesis that efficient preemptive ‘induction’ CD20(+) B-cell depletion consistently modulates pathogenic alloimmunity and attenuates CAV in this translational model, extending our prior findings with CNIs to the context of CD154 blockade