Kondo effect in double quantum dots with inter-dot repulsion

We investigate a symmetrical double quantum dot system serially attached to the leads. The emphasis is on the numerical analysis of finite inter-dot tunneling in the presence of inter-dot repulsive capacitive coupling. The results reveal the competition between extended Kondo phases and local singlet phases in spin and charge degrees of freedom. The corresponding phase diagram is determined quantitatively.Comment: 4 pages, 4 figure

Entanglement between static and flying qubits in quantum wires

A weakly bound electron in a semiconductor quantum wire is shown to become entangled with an itinerant electron via the coulomb interaction. The degree of entanglement and its variation with energy of the injected electron, may be tuned by choice of spin and initial momentum. Full entanglement is achieved close to energies where there are spin-dependent resonances. Possible realisations of related device structures are discussed

Consecutive earthquakes temporarily restructured the zooplankton community in an Alpine Lake

Two consecutive earthquakes temporary changed a zooplankton community in a high-mountain Lake Krn (altitude 1383 m a.s.l.). It was dominated by the eurytherm copepod, Cyclops vicious, until 1998, when the first earthquake hit the lake (EMS = 5.6). After the earthquake, the population of C. vicious collapsed and the thermophilic cladoceran, Ceriodaphnia quadrangula, took over. After the second earthquake in 2004 (EMS = 4.0), C. vicious became untraceable. In 2008, few copepods reappeared and by 2010 they became the sole dominant again. Only Secchi-disc depth showed a statistically significant increase over time, while P,, and temperature showed an increasing trend, yet the relationship was insignificant. To compare multi-parameter properties of the water column, the studied period was divided into Period 1 (before the first earthquake). Period 2 (between earthquakes) and Period 3 (after the second earthquake). A Hotteling T-2 test confirmed a statistically significant difference between Periods 1 and 2 & 3 (P 0.1). During simple laboratory experiment, specimens of C. vicious were covered with a thin layer of sediment, to mimic the earthquake's effect on their survival. A hypothesis was that the timing of both earthquakes had been crucial for decimation of C. vicious population as they re-suspended sediment with hibernating copepodites. As these became subsequently buried they were deprived of a re-activation signal and exposed prolonged anoxic conditions there. C. quadrangula temporary filled the void left by the copepod, which needed 6 years to regain its dominance

Kondo effect in triple quantum dots

Numerical analysis of the simplest odd-numbered system of coupled quantum dots reveals an interplay between magnetic ordering, charge fluctuations and the tendency of itinerant electrons in the leads to screen magnetic moments. The transition from local-moment to molecular-orbital behavior is visible in the evolution of correlation functions as the inter-dot coupling is increased. Resulting novel Kondo phases are presented in a phase diagram which can be sampled by measuring the zero-bias conductance. We discuss the origin of the even-odd effects by comparing with the double quantum dot.Comment: 4 pages, 4 figure

Conductance of a double quantum dot with correlation-induced wave function renormalization

The zero-temperature conductance of diatomic molecule, modelled as a correlated double quantum dot attached to noninteracting leads is investigated. We utilize the Rejec-Ramsak formulas, relating the linear-response conductance to the ground-state energy dependence on magnetic flux within the framework of EDABI method, which combines exact diagonalization with ab initio calculations. The single-particle basis renormalization leads to a strong particle-hole asymmetry, of the conductance spectrum, absent in a standard parametrized model study. We also show, that the coupling to leads V=0.5t (t is the hopping integral) may provide the possibility for interatomic distance manipulation due to the molecule instability.Comment: Presented on the The International Conference on Strongly Correlated Electron Systems SCES'05, July 26-30th 2005, Vienna, Austria. An abbreviated version will appear in Physica

Conductance of deformable molecules with interaction

Zero temperature linear response conductance of molecules with Coulomb interaction and with various types of phonon modes is analysed together with local occupation, local moment, charge fluctuations and fluctuations of molecular deformation. Deformation fluctuations are quantitatively related to charge fluctuations which exhibit similarity also to static charge susceptibility.Comment: 4 pages, color figure

Kondo effect in oscillating molecules

We consider electronic transport through break-junctions bridged by a single molecule in the Kondo regime. We describe the system by a two-channel Anderson model. We take the tunneling matrix elements to depend on the position of the molecule. It is shown, that if the modulation of the tunneling by displacement is large, the potential confining the molecule to the central position between the leads is softened and the position of the molecule is increasingly susceptible to external perturbations that break the inversion symmetry. In this regime, the molecule is attracted to one of the leads and as a consequence the conductance is small. We argue on semi-classical grounds why the softening occurs and corroborate our findings by numerical examples obtained by Wilson's numerical renormalization group and Schoenhammer-Gunnarsson's variational method.Comment: 5 p., Ustron'08 conference contributio