Państwa i narody pogranicza. Charakterystyka geopolityczna ziem i społeczeństw północno-wschodniej Europy w pracach Voltaire’a Histoire de Charles XII, roi de Suède i Montesquieu De l'esprit des lois

Zadanie pt. Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki nr 885/P-DUN/2014 zostało dofinansowane ze środków MNiSW w ramach działalności upowszechniającej naukę

Universal Scaling in Non-equilibrium Transport Through a Single-Channel Kondo Dot

Scaling laws and universality play an important role in our understanding of critical phenomena and the Kondo effect. Here we present measurements of non-equilibrium transport through a single-channel Kondo quantum dot at low temperature and bias. We find that the low-energy Kondo conductance is consistent with universality between temperature and bias and characterized by a quadratic scaling exponent, as expected for the spin-1/2 Kondo effect. The non-equilibrium Kondo transport measurements are well-described by a universal scaling function with two scaling parameters.Comment: v2: improved introduction and theory-experiment comparsio

Engineering the Kondo and Fano effects in double quantum dots

We demonstrate delicate control over the Kondo effect and its interplay with quantum interference in an Aharonov-Bohm interferometer containing one Kondo dot and one noninteracting dot. It is shown that the Kondo resonance undergoes a dramatic evolution as the interdot tunnel coupling progressively increases. A novel triple Kondo splitting occurs from the interference between constant and Lorentzian conduction bands that cooperate in forming the Kondo singlet. The device also manifests a highly controllable Fano-Kondo effect in coherent electronic transport, and can be tuned to a regime where the coupled dots behave as decoupled dots.Comment: 5 pages, 4 figure

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 previously thought to be well described without invoking Coulomb interactions. At temperatures below 50 mK we observe a periodic oscillation in the conductance of the dot with gate voltage that corresponds 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.Comment: Text and supplementary information. Text: 4 pages, 4 figures. Supplementary information: 4 pages, 4 figure

Spatially probed electron-electron scattering in a two-dimensional electron gas

Using scanning gate microscopy (SGM), we probe the scattering between a beam of electrons and a two-dimensional electron gas (2DEG) as a function of the beam's injection energy, and distance from the injection point. At low injection energies, we find electrons in the beam scatter by small-angles, as has been previously observed. At high injection energies, we find a surprising result: placing the SGM tip where it back-scatters electrons increases the differential conductance through the system. This effect is explained by a non-equilibrium distribution of electrons in a localized region of 2DEG near the injection point. Our data indicate that the spatial extent of this highly non-equilibrium distribution is within ~1 micrometer of the injection point. We approximate the non-equilibrium region as having an effective temperature that depends linearly upon injection energy.Comment: 8 pages, 6 figure

Persistent currents through a quantum impurity: Protection through integrability

We consider an integrable model of a one-dimensional mesoscopic ring with the conduction electrons coupled by a spin exchange to a magnetic impurity. A symmetry analysis based on a Bethe Ansatz solution of the model reveals that the current is insensitive to the presence of the impurity. We argue that this is true for any integrable impurity-electron interaction, independent of choice of physical parameters or couplings. We propose a simple physical picture of how the persistent current gets protected by integrability.Comment: 5 pages, minor update

Non-equilibrium transport theory of the singlet-triplet transition: perturbative approach

We use a simple iterative perturbation theory to study the singlet-triplet (ST) transition in lateral and vertical quantum dots, modeled by the non-equilibrium two-level Anderson model. To a great surprise, the region of stable perturbation theory extends to relatively strong interactions, and this simple approach is able to reproduce all experimentally-observed features of the ST transition, including the formation of a dip in the differential conductance of a lateral dot indicative of the two-stage Kondo effect, or the maximum in the linear conductance around the transition point. Choosing the right starting point to the perturbation theory is, however, crucial to obtain reliable and meaningful results