2,644 research outputs found
Quantum correlations in nanostructured two-impurity Kondo systems
We study the ground-state entanglement properties of nanostructured Kondo
systems consisting of a pair of impurity spins coupled to a background of
confined electrons. The competition between the RKKY-like coupling and the
Kondo effect determines the development of quantum correlations between the
different parts of the system. A key element is the electronic filling due to
confinement. An even electronic filling leads to results similar to those found
previously for extended systems, where the properties of the reduced
impurity-spin subsystem are uniquely determined by the spin correlation
function defining a one-dimensional phase space. An odd filling, instead,
breaks spin-rotation symmetry unfolding a two-dimensional phase space showing
rich entanglement characteristics as, e.g., the requirement of a larger amount
of entanglement for the development of non-local correlations between impurity
spins. We check these results by numerical simulations of elliptic quantum
corrals with magnetic impurities at the foci as a case study.Comment: Submitted for publication. 8 pages, 4 figures. Revised versio
Spin filters with Fano dots
We compute the zero bias conductance of electrons through a single ballistic
channel weakly coupled to a side quantum dot with Coulomb interaction. In
contrast to the standard setup which is designed to measure the transport
through the dot, the channel conductance reveals Coulomb blockade dips rather
then peaks due to the Fano-like backscattering. At zero temperature the Kondo
effect leads to the formation of broad valleys of small conductance
corresponding to an odd number of electrons on the dot. By applying a magnetic
field in the dot region we find two dips corresponding to a total suppression
in the conductance of spins up and down separated by an energy of the order of
the Coulomb interaction. This provides a possibility of a perfect spin filter.Comment: 5 pages, 4 figures, to be published in European Physical Journal
Mott transition in the Hubbard model away from particle-hole symmetry
We solve the Dynamical Mean Field Theory equations for the Hubbard model away
from the particle-hole symmetric case using the Density Matrix Renormalization
Group method. We focus our study on the region of strong interactions and
finite doping where two solutions coexist. We obtain precise predictions for
the boundaries of the coexistence region. In addition, we demonstrate the
capabilities of this precise method by obtaining the frequency dependent
optical conductivity spectra.Comment: 4 pages, 4 figures; updated versio
Mitochondrial heat-shock protein hsp60 is essential for assembly of proteins imported into yeast mitochondria
A nuclear encoded mitochondrial heat-shock protein hsp60 is required for the assembly into oligomeric complexes of proteins imported into the mitochondrial matrix. hsp60 is a member of the 'chaperonin' class of protein factors, which include the Escherichia coli groEL protein and the Rubisco subunit-binding protein of chloroplast
Dynamical Mean Field Theory with the Density Matrix Renormalization Group
A new numerical method for the solution of the Dynamical Mean Field Theory's
self-consistent equations is introduced. The method uses the Density Matrix
Renormalization Group technique to solve the associated impurity problem. The
new algorithm makes no a priori approximations and is only limited by the
number of sites that can be considered. We obtain accurate estimates of the
critical values of the metal-insulator transitions and provide evidence of
substructure in the Hubbard bands of the correlated metal. With this algorithm,
more complex models having a larger number of degrees of freedom can be
considered and finite-size effects can be minimized.Comment: 5 pages, 4 figure
Targeted Excited State Algorithms
To overcome the limitations of the traditional state-averaging approaches in
excited state calculations, where one solves for and represents all states
between the ground state and excited state of interest, we have investigated a
number of new excited state algorithms. Building on the work of van der Vorst
and Sleijpen (SIAM J. Matrix Anal. Appl., 17, 401 (1996)), we have implemented
Harmonic Davidson and State-Averaged Harmonic Davidson algorithms within the
context of the Density Matrix Renormalization Group (DMRG). We have assessed
their accuracy and stability of convergence in complete active space DMRG
calculations on the low-lying excited states in the acenes ranging from
naphthalene to pentacene. We find that both algorithms offer increased accuracy
over the traditional State-Averaged Davidson approach, and in particular, the
State-Averaged Harmonic Davidson algorithm offers an optimal combination of
accuracy and stability in convergence
Spin order in the one-dimensional Kondo and Hund lattices
We study numerically the one-dimensional Kondo and Hund lattices consisting
of localized spins interacting antiferro or ferromagnetically with the
itinerant electrons, respectively. Using the Density Matrix Renormalization
Group we find, for both models and in the small coupling regime, the existence
of new magnetic phases where the local spins order forming ferromagnetic
islands coupled antiferromagnetically. Furthermore, by increasing the
interaction parameter we find that this order evolves toward the
ferromagnetic regime through a spiral-like phase with longer characteristic
wave lengths. These results shed new light on the zero temperature magnetic
phase diagram for these models.Comment: PRL, to appea
Uniqueness and Non-uniqueness in the Einstein Constraints
The conformal thin sandwich (CTS) equations are a set of four of the Einstein
equations, which generalize the Laplace-Poisson equation of Newton's theory. We
examine numerically solutions of the CTS equations describing perturbed
Minkowski space, and find only one solution. However, we find {\em two}
distinct solutions, one even containing a black hole, when the lapse is
determined by a fifth elliptic equation through specification of the mean
curvature. While the relationship of the two systems and their solutions is a
fundamental property of general relativity, this fairly simple example of an
elliptic system with non-unique solutions is also of broader interest.Comment: 4 pages, 4 figures; abstract and introduction rewritte
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