468 research outputs found
Even-odd correlations in capacitance fluctuations of quantum dots
We investigate effects of short range interactions on the addition spectra of
quantum dots using a disordered Hubbard model. A correlation function \cS(q) is
defined on the inverse compressibility versus filling data, and computed
numerically for small lattices. Two regimes of interaction strength are
identified: the even/odd fluctuations regime typical of Fermi liquid ground
states, and a regime of structureless \cS(q) at strong interactions. We
propose to understand the latter regime in terms of magnetically correlated
localized spins.Comment: 3 pages, Revtex, Without figure
Absence of bimodal peak spacing distribution in the Coulomb blockade regime
Using exact diagonalization numerical methods, as well as analytical
arguments, we show that for the typical electron densities in chaotic and
disordered dots the peak spacing distribution is not bimodal, but rather
Gaussian. This is in agreement with the experimental observations. We attribute
this behavior to the tendency of an even number of electrons to gain on-site
interaction energy by removing the spin degeneracy. Thus, the dot is predicted
to show a non trivial electron number dependent spin polarization. Experimental
test of this hypothesis based on the spin polarization measurements are
proposed.Comment: 13 pages, 3 figures, accepted for publication in PRL - a few small
change
Density Modulations and Addition Spectra of Interacting Electrons in Disordered Quantum Dots
We analyse the ground state of spinless fermions on a lattice in a weakly
disordered potential, interacting via a nearest neighbour interaction, by
applying the self-consistent Hartree-Fock approximation. We find that charge
density modulations emerge progressively when r_s >1, even away from
half-filling, with only short-range density correlations. Classical geometry
dependent "magic numbers" can show up in the addition spectrum which are
remarkably robust against quantum fluctuations and disorder averaging.Comment: 4 pages, 3 eps figure
ΠΠΏΡΠΈΠΌΠΈΠ·Π°ΡΠΈΠΎΠ½Π½ΡΠ΅ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΡΠ΅ΡΠΊΠΈΠ΅ Π·Π°Π΄Π°ΡΠΈ Π² ΡΠΈΡΡΠ΅ΠΌΠ°Ρ Π·Π°ΡΠΈΡΡ ΠΈΠ½ΡΠΎΡΠΌΠ°ΡΠΈΠΈ
Π ΠΎΠ·ΡΠΎΠ±Π»Π΅Π½ΠΎ ΠΌΠ°ΡΠ΅ΠΌΠ°ΡΠΈΡΠ½Ρ ΠΌΠΎΠ΄Π΅Π»Ρ Ρ ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊΡ Π²ΠΈΠ·Π½Π°ΡΠ΅Π½Π½Ρ ΠΎΠΏΡΠΈΠΌΠ°Π»ΡΠ½ΠΎΠ³ΠΎ ΡΠΎΠ·ΠΏΠΎΠ΄ΡΠ»Ρ ΡΠ΅ΡΡΡΡΡΠ² ΠΌΡΠΆ ΠΎΠ±βΡΠΊΡΠ°ΠΌΠΈ Π·Π°Ρ
ΠΈΡΡΡ ΡΠ½ΡΠΎΡΠΌΠ°ΡΡΡ. Π‘ΡΠΎΡΠΌΡΠ»ΡΠΎΠ²Π°Π½ΠΎ ΡΡΠ»ΡΠΎΠ²Ρ ΡΡΠ½ΠΊΡΡΡ, Π½Π° ΠΎΡΠ½ΠΎΠ²Ρ ΡΠΊΠΎΡ ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½ΠΎ ΡΠ»ΡΡΡΡΠ°ΡΠΈΠ²Π½Ρ ΡΠΎΠ·ΡΠ°Ρ
ΡΠ½ΠΊΠΈ Π² ΡΠΈΡΡΠ΅ΠΌΡ Π· Π΄Π²ΠΎΡ
ΡΠ½ΡΠΎΡΠΌΠ°ΡΡΠΉΠ½ΠΈΡ
ΠΎΠ±βΡΠΊΡΡΠ². ΠΠΊΡΠ΅ΡΠ»Π΅Π½ΠΎ Π½Π°ΠΏΡΡΠΌΠΊΠΈ ΡΠΎΠ·Π²ΠΈΡΠΊΡ Π·Π°ΠΏΡΠΎΠΏΠΎΠ½ΠΎΠ²Π°Π½ΠΎΡ ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊΠΈ.The mathematical model and method of determination of the optimal distribution of the resources between the objects of data security are developed. A criterion function on the basis of which the illustrative calculations in a system of two information objects were done, is formulated. The directions of the proposed method development are outlined.Π Π°Π·ΡΠ°Π±ΠΎΡΠ°Π½Π° ΠΌΠ°ΡΠ΅ΠΌΠ°ΡΠΈΡΠ΅ΡΠΊΠ°Ρ ΠΌΠΎΠ΄Π΅Π»Ρ ΠΈ ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊΠ° ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΡ ΠΎΠΏΡΠΈΠΌΠ°Π»ΡΠ½ΠΎΠ³ΠΎ ΡΠ°ΡΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΡ ΡΠ΅ΡΡΡΡΠΎΠ² ΠΌΠ΅ΠΆΠ΄Ρ ΠΎΠ±ΡΠ΅ΠΊΡΠ°ΠΌΠΈ Π·Π°ΡΠΈΡΡ ΠΈΠ½ΡΠΎΡΠΌΠ°ΡΠΈΠΈ. Π‘ΡΠΎΡΠΌΡΠ»ΠΈΡΠΎΠ²Π°Π½Π° ΡΠ΅Π»Π΅Π²Π°Ρ ΡΡΠ½ΠΊΡΠΈΡ, Π½Π° ΠΎΡΠ½ΠΎΠ²Π΅ ΠΊΠΎΡΠΎΡΠΎΠΉ ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½ΠΎ ΠΈΠ»Π»ΡΡΡΡΠ°ΡΠΈΠ²Π½ΡΠ΅ ΡΠ°ΡΡΠ΅ΡΡ Π² ΡΠΈΡΡΠ΅ΠΌΠ΅ ΠΈΠ· Π΄Π²ΡΡ
ΠΈΠ½ΡΠΎΡΠΌΠ°ΡΠΈΠΎΠ½Π½ΡΡ
ΠΎΠ±ΡΠ΅ΠΊΡΠΎΠ². ΠΡΠ΅ΡΡΠ΅Π½Ρ Π½Π°ΠΏΡΠ°Π²Π»Π΅Π½ΠΈΡ ΡΠ°Π·Π²ΠΈΡΠΈΡ ΠΏΡΠ΅Π΄Π»ΠΎΠΆΠ΅Π½Π½ΠΎΠΉ ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊΠΈ
The International Long Term Ecological Research Network: a platform for collaboration
Many scientists around the world became interested in the U.S. Long Term Ecological Research (U.S. LTER) Network\u27s research model during the 1990s and began to develop LTER and Long Term Socio-ecological Research networks in their own countries. These local networks, including the U.S. LTER Network, were loosely federated in 1993 to form the International Long Term Ecological Research (ILTER) Network, a βnetwork of networks.β Although the first 10 yr of ILTER Network activities were largely supported by funds from the U.S. National Science Foundation, the ILTER Network had transformed into a robust, self-sustaining entity by 2006 following a two-year strategic planning process. The goal of the ILTER Network is to improve understanding of how pressures such as climate change and land use affect global ecosystems in order to inform solutions to current and future environmental problems. To fulfill this mission, the ILTER Network fosters collaborations among member scientists to extend the scope of their research across disciplinary boundaries and across more of the ILTER\u27s 600+ research sites. The ILTER Network also has many long-term data sets that are freely available for use by students, scientists, and policymakers all over the world. In this collection of papers, we consider how the ILTER Network has been, and will be, leveraged by U.S. researchers to advance understanding of ecological and socio-ecological systems around the globe
Spin magnetization of strongly correlated electron gas confined in a two-dimensional finite lattice
The influence of disorder and interaction on the ground state polarization of
the two-dimensional (2D) correlated electron gas is studied by numerical
investigations of unrestricted Hartree-Fock equations. The ferromagnetic ground
state is found to be plausible when the electron number is lowered and the
interaction and disorder parameters are suitably chosen. For a finite system at
constant electronic density the disorder induced spin polarization is cut off
when the electron orbitals become strongly localized to the individual network
sites. The fluctuations of the interaction matrix elements are calculated and
brought out as favoring the ferromagnetic instability in the extended and weak
localization regime. The localization effect of the Hubbard interaction term is
discussed.Comment: 7 pages, 9 figure
Mesoscopic fluctuations of the ground state spin of a small metal particle
We study the statistical distribution of the ground state spin for an
ensemble of small metallic grains, using a random-matrix toy model. Using the
Hartree Fock approximation, we find that already for interaction strengths well
below the Stoner criterion there is an appreciable probability that the ground
state has a finite, nonzero spin. Possible relations to experiments are
discussed.Comment: 4 pages, RevTeX; 1 figure included with eps
Ground-state energy and spin in disordered quantum dots
We investigate the ground-state energy and spin of disordered quantum dots
using spin-density-functional theory. Fluctuations of addition energies
(Coulomb-blockade peak spacings) do not scale with average addition energy but
remain proportional to level spacing. With increasing interaction strength, the
even-odd alternation of addition energies disappears, and the probability of
non-minimal spin increases, but never exceeds 50%. Within a two-orbital model,
we show that the off-diagonal Coulomb matrix elements help stabilize a ground
state of minimal spin.Comment: 10 pages, 2 figure
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