Coulomb quantum kinetics in pulse-excited semiconductors

The quantum kinetic equations of the electron and hole densities and the interband polarization are derived for a laser-pulse-excited semiconductor with Coulomb interaction including renormalization effects, excitonic effects and scattering with memory kernels. Numerical solutions of this set of non-Markovian, nonlinear integro-differential equations are obtained for a statically screened Coulomb potential.     

Non-Lorentzian spectral functions for Coulomb quantum kinetics

Numerical solutions of the Kadanoff-Baym equations with self-energies in second Born approximation are presented for electrons in a bulk semiconductor. The results are used to analyze in detail the two-time spectral function .In particular, (I) the damping of the spectral function is investigated over a broad density range both, for low and high temperatures; (II), is compared to analytical expressions - an exponential and a recently proposed inverse hyperbolic cosine decay law; (III), the two analytical spectral functions are studied with respect to conservation of total energy, where for the inverse hyperbolic cosine an improved behavior is demonstrated. Received 7 August 1998     

Quantum-kinetic theory of hot luminescence from pulse-excited semiconductors

A theory of time-resolved luminescence from photoexcited semiconductors is presented. It combines quantum kinetics of hot-carrier relaxation and quantum theory of spontaneous emission. Model calculations show the "transfer" of photoluminescence from the initial signal at the pump frequency via subsequent phonon replicas until the buildup of luminescence at the excitonic resonance. Time-resolved photoluminescence is predicted to be a sensitive measure of electron-LO-phonon quantum kinetics and bottleneck effects.     

Coulomb effects and thermopower in elemental covalent amorphous semiconductors

It is shown that the Coulomb effects resulting in a single-occupancy of localized states in the vicinity of the chemical potential in the mobility gap yield a simple possibility to explain both the magnitude and the temperature insensitiveness of the thermoelectric power of amorphous Ge and Si in the phonon-assisted hopping regime observed at low temperatures.The main physical ideas of this work resulted from a collaboration with Drs. A.Aldea and L.Bányai (see ref. [28]). The present author acknowledges with pleasure their significant contribution to this work.     

Coulomb effects in semiconductor quantum dots

This paper presents a new model for the Internet graph (AS graph) based on the concept of heuristic trade-off optimization, introduced by Fabrikant, Koutsoupias and Papadimitriou in [5] to grow a random tree with a heavily tailed degree distribution. We propose here a generalization of this approach to generate a general graph, as a candidate for modeling the Internet. We present the results of our simulations and an analysis of the standard parameters measured in our model, compared with measurements from the physical Internet graph.Received: 9 February 2004, Published online: 14 May 2004PACS: 89.75.-k Complex systems - 89.75.Hc Networks and genealogical trees - 89.75.Da Systems obeying scaling laws - 89.75.Fb Structures and organization in complex systems - 89.65.Gh Economics; econophysics, financial markets, business and managementLRI: http: //www.lri.fr/~ihameli; CNRS, LIP, ENS Lyon : http: //www.ens-lyon.fr/~nschaban     

Coulomb blockade in molecular quantum dots

The rate-equation approach is used to describe sequential tunneling through a molecular junction in the Coulomb blockade regime. Such device is composed of molecular quantum dot (with discrete energy levels) coupled with two metallic electrodes via potential barriers. Based on this model, we calculate nonlinear transport characteristics (conductance-voltage and current-voltage dependences) and compare them with the results obtained within a self-consistent field approach. It is shown that the shape of transport characteristics is determined by the combined effect of the electronic structure of molecular quantum dots and by the Coulomb blockade. In particular, the following phenomena are discussed in detail: the suppression of the current at higher voltages, the charging-induced rectification effect, the charging-generated changes of conductance gap and the temperature-induced as well as broadening-generated smoothing of current steps.     

Coulomb blockade in an open quantum dot

We report the observation of Coulomb blockade in a quantum dot contacted by two quantum point contacts each with a single fully transmitting mode, a system thought to be well described without invoking Coulomb interactions. Below 50 mK we observe a periodic oscillation in the conductance of the dot with gate voltage, corresponding to a residual quantization of charge. From the temperature and magnetic field dependence, we infer the oscillations are mesoscopic Coulomb blockade, a type of Coulomb blockade caused by electron interference in an otherwise open system.     

Coulomb oscillations in partially open quantum dots

We report tunneling measurements of the Coulomb blockade in a single quantum dot at zero magnetic field and dilution refrigerator temperatures with weak tunneling from the dot to one lead (the ‘closed’ lead, conductanceG_closed) and strong tunneling to the other lead (the ‘open’ lead, conductanceG_open). We observe suppression of the Coulomb oscillations withG_open≈2e²/h, and then see the oscillations return forG_open>2e²/h. The oscillations show a strikingly lower threshold temperature atG_open≈2e²/hthan for greater or lesserG_open.     

Weak Coulomb blockade effect in quantum dots

We develop the general nonequilibrium theory of transport through a quantum dot, including Coulomb blockade effects via a 1/N expansion, where N is the number of scattering channels. At lowest order we recover the Landauer formula for the current plus a self-consistent equation for the dot potential. We obtain the leading corrections and compare with earlier approaches. Finally, we show that to leading and to next leading order in 1/N there is no interaction correction to the weak localization, in contrast to previous theories, but consistent with experiments by Huibers et al. [Phys. Rev. Lett. 81, 1917 (1998)], where N=4.     

Two-species Coulomb chains for quantum information

We study from the point of view of quantum information the properties of the collective oscillations of a linear chain of ions trapped in a linear Paul trap and composed of two ion species. We discuss extensively sympathetic cooling of the chain and the effect of anharmonicity on laser-cooling and quantum-information processing. Received 19 May 2000     

Coulomb bound potential quantum rod qubit

We study the eigenenergies and the eigenfunctions of the ground and the first excited states of an electron, which is strongly coupled to LO-phonon in a quantum rod with a hydrogen-like impurity at the center by using the variational method of Pekar type. This quantum rod system may be used as a two-level quantum qubit. When the electron is in the superposition state of the ground and the first-excited states, the probability density of the electron oscillates in the quantum rod. It is found that the probability density and the oscillation period are individually increased and decreased due to the presence of the Coulomb interaction between the electron and the hydrogen-like impurity. The oscillation period is an increasing function of the ellipsoid aspect ratio and the effective confinement lengths of the quantum rod, whereas it is a decreasing one of the electron–phonon coupling strength.     

Phonon-assisted auger recombination in quantum well semiconductors

Phonon-assisted Auger recombination (AR) is shown to be an important loss mechanism in a quantum well semiconductor in addition to the direct AR. Theoretical investigations demonstrate that it is of the same order of magnitude and has the same temperature dependence as in bulk material, just as direct AR, provided that the material parameters and the carrier concentrations are the same as in the bulk.