103 research outputs found
Minimal realization of the Orbital Kondo effect in a Quantum Dot with two Leads
We demonstrate theoretically how the Kondo effect may be observed in the
transport of spinless electrons through a quantum dot. The role of conduction
electron spin is played by a lead index. The Kondo effect takes place if there
are two close levels in the dot populated by a single electron. For
temperatures exceeding the Kondo temperature the conductance is
maximal if the levels are exactly degenerate. However, at zero temperature the
conductance is zero at the SU(2) symmetric point, but reaches the unitary limit
for some finite value of the level splitting \Delta\eps\sim T_K.
Introducing the spin-1/2 for electrons and having two degenerate orbital levels
in the dot allows to observe the SU(4) Kondo effect in a single dot coupled to
two leads.Comment: 6 pages, 2 figure
Investigation of the coupling asymmetries at double-slit interference experiments
Double-slit experiments inferring the phase and the amplitude of the
transmission coefficient performed at quantum dots (QD), in the Coulomb
blockade regime, present anomalies at the phase changes depending on the number
of electrons confined. This phase change cannot be explained if one neglects
the electron-electron interactions. Here, we present our numerical results,
which simulate the real sample geometry by solving the Poisson equation in 3D.
The screened potential profile is used to obtain energy eigenstates and
eigenvalues of the QD. We find that, certain energy levels are coupled to the
leads stronger compared to others. Our results give strong support to the
phenomenological models in the literature describing the charging of a QD and
the abrupt phase changes.Comment: conference paper, 50th anniversary of Aharonov-Bohm effec
Vortices in a cylinder: Localization after depinning
Edge effects in the depinned phase of flux lines in hollow superconducting
cylinder with columnar defects and electric current along the cylinder are
investigated. Far from the ends of the cylinder vortices are distributed almost
uniformly (delocalized). Nevertheless, near the edges these free vortices come
closer together and form well resolved dense bunches. A semiclassical picture
of this localization after depinning is described. For a large number of
vortices their density has square root singularity at the border of
the bunch ( is semicircle in the simplest case). However, by tuning
the strength of current, the various singular regimes for may be
reached. Remarkably, this singular behaviour reproduces the phase transitions
discussed during the past decade within the random matrix regularization of
2d-Gravity.Comment: 4 pages, REVTEX, 2 eps figure
The Enhanced Sensitivity of the Transmission Phase of a Quantum Dot to Kondo Correlations
The strong sensitivity of the transmission phase through a quantum dot
embedded into one arm of a two-wave Aharonov-Bohm interferometer to the Kondo
effect is explained. The enhancement takes place because of the buildup of the
exchange scattering on the dot due to Kondo correlations even much above
. The enhanced exchange competes with the potential scattering, which is
always weak. Both cases of the Anderson impurity model and a multilevel quantum
dot are considered. In the latter case in addition to the description of
peculiar phase behavior a mechanism leading to ferromagnetic Kondo coupling in
quantum dots is proposed.Comment: 4 pages, 2 figure
Ehrenfest time dependent suppression of weak localization
The Ehrenfest time dependence of the suppression of the weak localization
correction to the conductance of a {\em clean} chaotic cavity is calculated.
Unlike in earlier work, no impurity scattering is invoked to imitate
diffraction effects. The calculation extends the semiclassical theory of K.
Richter and M. Sieber [Phys. Rev. Lett. {\bf 89}, 206801 (2002)] to include the
effect of a finite Ehrenfest time.Comment: 3 Pages, 1 Figure, RevTe
ENSURING ECONOMIC SECURITY OF RUSSIA IN THE CONTEXT OF AFRICAN DEVELOPMENT TRENDS: PROBLEMS AND PROSPECTS
Abstract
Purpose: A new scientific problem is posed and substantiated: the need to take into account the African economic development trends in the system of ensuring the economic security of Russia. In this context, in order to assess the security of the national economy and the competitive position of Russia, the results of scientific studies of the main development trends and threats in Africa, the position of various countries on the African continent are analyzed.
Methodology: The authors are based on the analysis of current scientific literature, government official documents, and statistical reports. The main methods of research are analytical review, comparison, systematic approach, cultural and civilizational approach.
Result: The article substantiates the position that taking into account the development trends of the African continent is an important component in the system of assessing the national economic security of Russia in the current period and in the future, ensuring competitiveness and strengthening the economic sovereignty of Russia, analyzing the potential of interaction with African countries in the management practice.
Applications: This research can be used for the universities, teachers and education students.
Novelty/Originality: The authors formulate the main directions of the activation of scientific research and concentration of practical efforts to improve the national economic security of Russia in the context of the development trend of the African continent
Chaos Thresholds in finite Fermi systems
The development of Quantum Chaos in finite interacting Fermi systems is
considered. At sufficiently high excitation energy the direct two-particle
interaction may mix into an eigen-state the exponentially large number of
simple Slater-determinant states. Nevertheless, the transition from Poisson to
Wigner-Dyson statistics of energy levels is governed by the effective high
order interaction between states very distant in the Fock space. The concrete
form of the transition depends on the way one chooses to work out the problem
of factorial divergency of the number of Feynman diagrams. In the proposed
scheme the change of statistics has a form of narrow phase transition and may
happen even below the direct interaction threshold.Comment: 9 pages, REVTEX, 2 eps figures. Enlarged versio
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