Página 1 dos resultados de 231 itens digitais encontrados em 0.163 segundos

## Carbon Nanotubes for the Generation and Imaging of Interacting 1D States of Matter

Fonte: Harvard University
Publicador: Harvard University

Tipo: Thesis or Dissertation

EN_US

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#Condensed matter physics#Nanoscience#Nanotechnology#Carbon nanotubes#Charge detectors#Nanoassembly#Nanofabrication#Quantum dots#Scanning probes

Low-dimensional systems in condensed matter physics exhibit a rich array of correlated electronic phases. One-dimensional systems stand out in this regard. Electrons cannot avoid each other in 1D, enhancing the effects of interactions. The resulting correlations leave distinct spatial imprints on the electronic density that can be imaged with scanning probes. Disorder, however, can destroy these delicate interacting states by breaking up the electron liquid into localized pieces. Thus, to generate fragile interacting quantum states, one requires an extremely clean system in which disorder does not overcome interactions, as well as a high degree of tunability to design potential landscapes. Furthermore, to directly measure the resulting spatial correlations, one requires an exceptionally sensitive scanning probe, but the most sensitive probes presently available are also invasive, perturbing the system and screening electron-electron interactions.; Engineering and Applied Sciences

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## The transfer of energy between electrons and ions in solids

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 20/03/2006

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In this review we consider those processes in condensed matter that involve
the irreversible flow of energy between electrons and nuclei that follows from
a system being taken out of equilibrium. We survey some of the more important
experimental phenomena associated with these processes, followed by a number of
theoretical techniques for studying them. The techniques considered are those
that can be applied to systems containing many non-equivalent atoms. They
include both perturbative approaches (Fermi's Golden Rule, and non-equilibrium
Green's functions) and molecular dynamics based (the Ehrenfest approximation,
surface hopping, semi-classical gaussian wavefunction methods and correlated
electron-ion dynamics). These methods are described and characterised, with
indications of their relative merits.; Comment: LaTeX with IoP style files, 43 pages, 3 figures

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## A New Supersymmetric and Exactly Solvable Model of Correlated Electrons

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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A new lattice model is presented for correlated electrons on the unrestricted
$4^L$-dimensional electronic Hilbert space $\otimes_{n=1}^L{\bf C}^4$ (where
$L$ is the lattice length). It is a supersymmetric generalization of the
Hubbard model, but differs from the extended Hubbard model proposed by Essler,
Korepin and Schoutens. The supersymmetry algebra of the new model is
superalgebra $gl(2|1)$. The model contains one symmetry-preserving free real
parameter which is the Hubbard interaction parameter $U$, and has its origin
here in the one-parameter family of inequivalent typical 4-dimensional irreps
of $gl(2|1)$. On a one-dimensional lattice, the model is exactly solvable by
the Bethe ansatz.; Comment: 10 pages, LaTex. (final version to appear in Phys.Rev.Lett.)

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## The Phase Diagram of Correlated Electrons in a Lattice of Berry Molecules

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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A model for correlated electrons in a lattice with local additional spin--1
degrees of freedom inducing constrained hopping, is studied both in the low
density limit and at quarter filling. We show that in both 1D and 2D two
particles form a bound state even in presence of a repulsive U

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## Adiabatic Connection for Strictly-Correlated Electrons

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

65.68%

Modern density functional theory (DFT) calculations employ the Kohn-Sham (KS)
system of non-interacting electrons as a reference, with all complications
buried in the exchange-correlation energy (Exc). The adiabatic connection
formula gives an exact expression for Exc. We consider DFT calculations that
instead employ a reference of strictly-correlated electrons. We define a
"decorrelation energy" that relates this reference to the real system, and
derive the corresponding adiabatic connection formula. We illustrate this
theory in three situations, namely the uniform electron gas, Hooke's atom, and
the stretched hydrogen molecule. The adiabatic connection for
strictly-correlated electrons provides an alternative perspective for
understanding density functional theory and constructing approximate
functionals.; Comment: 4 figures, has been published in J. Chem. Phys

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## Integrability and coherence of hopping between 1D correlated electrons systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/08/1995

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We present numerical evidence that the hopping of electrons between chains
described by the $t-J$ model is coherent in the integrable cases ($J=0$ and
$J=2$) and essentially incoherent otherwise. This effect is {\it not} related
to the value of the exponent $\alpha$, (which is restricted to the interval
[0,1/8] when $0\le J\le 2$), and we propose that enhanced coherence is
characteristic of integrable systems.; Comment: 9 pages, LateX, 4 figures in uuencoded format, submitted to Phys.
Rev. Lett

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## Andreev-Tunneling, Coulomb Blockade, and Resonant Transport of Non-Local Spin-Entangled Electrons

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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We propose and analyze a spin-entangler for electrons based on an s-wave
superconductor coupled to two quantum dots each of which is tunnel-coupled to
normal Fermi leads. We show that in the presence of a voltage bias and in the
Coulomb blockade regime two correlated electrons provided by the Andreev
process can coherently tunnel from the superconductor via different dots into
different leads. The spin-singlet coming from the Cooper pair remains preserved
in this process, and the setup provides a source of mobile and nonlocal
spin-entangled electrons. The transport current is calculated and shown to be
dominated by a two-particle Breit-Wigner resonance which allows the injection
of two spin-entangled electrons into different leads at exactly the same
orbital energy, which is a crucial requirement for the detection of spin
entanglement via noise measurements. The coherent tunneling of both electrons
into the same lead is suppressed by the on-site Coulomb repulsion and/or the
superconducting gap, while the tunneling into different leads is suppressed
through the initial separation of the tunneling electrons. In the regime of
interest the particle-hole excitations of the leads are shown to be negligible.
The Aharonov-Bohm oscillations in the current are shown to contain single- and
two-electron periods with amplitudes that both vanish with increasing Coulomb
repulsion albeit differently fast.; Comment: 11 double-column pages...

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## Composite Fermion Description of Correlated Electrons in Quantum Dots: Low Zeeman Energy Limit

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 02/10/1995

Relevância na Pesquisa

55.5%

We study the applicability of composite fermion theory to electrons in
two-dimensional parabolically-confined quantum dots in a strong perpendicular
magnetic field in the limit of low Zeeman energy. The non-interacting composite
fermion spectrum correctly specifies the primary features of this system.
Additional features are relatively small, indicating that the residual
interaction between the composite fermions is weak. \footnote{Published in
Phys. Rev. B {\bf 52}, 2798 (1995).}; Comment: 15 pages, 7 postscript figures

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## Magnetic impurity coupled to interacting conduction electrons

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 12/10/1995

Relevância na Pesquisa

55.52%

We consider a magnetic impurity which interacts by hybridization with a
system of weakly correlated electrons and determine the energy of the ground
state by means of an 1/N_f expansion. The correlations among the conduction
electrons are described by a Hubbard Hamiltonian and are treated to lowest
order in the interaction strength. We find that their effect on the Kondo
temperature, T_K, in the Kondo limit is twofold: First, the position of the
impurity level is shifted due to the reduction of charge fluctuations, which
reduces T_K. Secondly, the bare Kondo exchange coupling is enhanced as spin
fluctuations are enlarged. In total, T_K increases. Both corrections require
intermediate states beyond the standard Varma-Yafet ansatz. This shows that the
Hubbard interaction does not just provide quasiparticles, which hybridize with
the impurity, but also renormalizes the Kondo coupling.; Comment: ReVTeX 19 pages, 3 uuenconded postscript figures

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## Superconductivity Near Phase Separation in Models of Correlated Electrons

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 20/09/1993

Relevância na Pesquisa

65.54%

Numerical and analytical studies of several models of correlated electrons
are discussed. Based on exact diagonalization and variational Monte Carlo
techniques, we have found strong indications that the two dimensional t-J model
superconducts near phase separation in the regime of quarter-filling density,
in agreement with previous results reported by Dagotto and Riera (Phys. Rev.
Letters 70, 682 (1993)). At this density the dominant channel is d_{x^2-y^2},
but a novel transition to s-wave superconductivity is observed decreasing the
electronic density. In addition, the one band t-U-V model has also been studied
using the mean-field approximation that accurately described the spin density
wave phase of the repulsive Hubbard model at half-filling. Finally, the two
band Hubbard model on a chain is also analyzed. Superconducting correlations
near phase separation exist in this model, as it occurs in the t-J model. Based
on these nontrivial examples it is $conjectured$ that electronic models tend to
have superconducting phases in the vicinity of phase separation.Reciprocally,
if it is established that a model that does not phase separate, then its
chances of presenting a superconducting phase are considerably reduced.; Comment: 29 pages...

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## New insights into electron spin dynamics in the presence of correlated noise

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

55.67%

The changes of the spin depolarization length in zinc-blende semiconductors
when an external component of correlated noise is added to a static driving
electric field are analyzed for different values of field strength, noise
amplitude and correlation time. Electron dynamics is simulated by a Monte Carlo
procedure which keeps into account all the possible scattering phenomena of the
hot electrons in the medium and includes the evolution of spin polarization.
Spin depolarization is studied by examinating the decay of the initial spin
polarization of the conduction electrons through the D'yakonov-Perel process,
the only relevant relaxation mechanism in III-V crystals. Our results show
that, for electric field amplitude lower than the Gunn field, the dephasing
length shortens with the increasing of the noise intensity. Moreover, a
nonmonotonic behavior of spin depolarization length with the noise correlation
time is found, characterized by a maximum variation for values of noise
correlation time comparable with the dephasing time. Instead, in high field
conditions, we find that, critically depending on the noise correlation time,
external fluctuations can positively affect the relaxation length. The
influence of the inclusion of the electron-electron scattering mechanism is
also shown and discussed.; Comment: Published on "Journal of Physics: Condensed Matter" as "Fast Track
Communications"...

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## RKKY interaction and Kondo screening cloud for correlated electrons

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 23/08/1996

Relevância na Pesquisa

65.54%

The RKKY law and the Kondo screening cloud around a magnetic impurity are
investigated for correlated electrons in 1D (Luttinger liquid). We find slow
algebraic distance dependences, with a crossover between both types of
behavior. Monte Carlo simulations have been developed to study this crossover.
In the strong coupling regime, the Knight shift is shown to increase with
distance due to correlations.; Comment: 5 pages REVTeX, incl two figures, to appear in Phys.Rev.B

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## Correlated Electron Pseudopotentials for 3d-Transition Metals

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 04/02/2015

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A recently published correlated electron pseudopotentials (CEPPs) method has
been adapted for application to the 3d-transition metals, and to include
relativistic effects. New CEPPs are reported for the atoms Sc$-$Fe, constructed
from atomic quantum chemical calculations that include an accurate description
of correlated electrons. Dissociation energies, molecular geometries, and
zero-point vibrational energies of small molecules are compared with all
electron results, with all quantities evaluated using coupled cluster singles
doubles and triples (CCSD(T)) calculations. The CEPPs give better results in
the correlated-electron calculations than Hartree-Fock-based pseudopotentials
available in the literature.; Comment: 12 pages, 6 figures

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## New integrable model of correlated electrons with off-diagonal long-range order from $so(5)$ symmetry

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 29/09/1998

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We present a new integrable model for correlated electrons which is based on
a $so(5)$ symmetry. By using an $\eta$-pairing realization we construct
eigenstates of the Hamiltonian with off-diagonal long-range order. It is also
shown that these states lie in the ground state sector. We exactly solve the
model on a one-dimensional lattice by the Bethe ansatz.; Comment: RevTex, 4 pages

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## The Hartree-Fock based diagonalization - an efficient algorithm for the treatment of interacting electrons in disordered solids

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 05/11/2001

Relevância na Pesquisa

55.6%

#Condensed Matter - Disordered Systems and Neural Networks#Condensed Matter - Mesoscale and Nanoscale Physics

The Hartree-Fock based diagonalization is a computational method for the
investigation of the low-energy properties of correlated electrons in
disordered solids. The method is related to the quantum-chemical configuration
interaction approach. It consists in diagonalizing the Hamiltonian in a reduced
Hilbert space built of the low-energy states of the corresponding disordered
Hartree-Fock Hamiltonian. The properties of the method are discussed for the
example of the quantum Coulomb glass, a lattice model of electrons in a random
potential interacting via long-range Coulomb interaction. Particular attention
is paid to the accuracy of the results as a function of the dimension of the
reduced Hilbert space. It is argued that disorder actually helps the
approximation.; Comment: 14 pages, 8 figures, plenary talk given by M. Schreiber at the 3rd
IMACS Seminar on Monte Carlo methods, Salzburg (September 10-14, 2001)

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## Correlated Electrons in Carbon Nanotubes

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

55.52%

Single-wall carbon nanotubes are almost ideal systems for the investigation
of exotic many-body effects due to non-Fermi liquid behavior of interacting
electrons in one dimension. Recent theoretical and experimental results are
reviewed with a focus on electron correlations. Starting from a microscopic
lattice model we derive an effective phase Hamiltonian for conducting
single-wall nanotubes with arbitrary chirality. The parameters of the
Hamiltonian show very weak dependence on the chiral angle, which makes the
low-energy physics of conducting nanotubes universal. The temperature-dependent
resistivity and frequency-dependent optical conductivity of nanotubes with
impurities are evaluated within the Luttinger-like model. Localization effects
are studied. In particular, we found that intra-valley and inter-valley
electron scattering can not coexist at low energies. Low-energy properties of
clean nanotubes are studied beyond the Luttinger liquid approximation. The
strongest Mott-like electron instability occurs at half filling. In the Mott
insulating phase electrons at different atomic sublattices form characteristic
bound states. The energy gaps of $0.01-0.1$ eV occur in all modes of elementary
excitations. We finally discuss observability of the Mott insulating phase in
transport experiments. The accent is made on the charge transfer from external
electrodes which results in a deviation of the electron density from
half-filling.; Comment: 16 pages...

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## Persistent current of correlated electrons in mesoscopic ring with impurity

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 06/12/2007

Relevância na Pesquisa

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The persistent current of correlated electrons in a continuous
one-dimensional ring with a single scatterer is calculated by solving the
many-body Schrodinger equation for several tens of electrons interacting via
the electron-electron (e-e) interaction of finite range. The problem is solved
by the configuration-interaction (CI) and diffusion Monte Carlo (DMC) methods.
The CI and DMC results are in good agreement. In both cases, the persistent
current $I$ as a function of the ring length $L$ exhibits the asymptotic
dependence $I \propto L^{-1-\alpha}$ typical of the Luttinger liquid, where the
power $\alpha$ depends only on the e-e interaction. The numerical values of
$\alpha$ agree with the known formula of the renormalisation-group theory.; Comment: Conference proceedings. Accepted for publication in Physica E

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## Fundamental noise in matter interferometers

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 28/03/2007

Relevância na Pesquisa

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These lecture notes discuss two effects which contribute to the reduction of
the interference fringe contrast in matter interferometers. The first effect is
the shot noise arising from a finite number of atoms used in experiments.
Focusing on a single shot measurement we provide explicit calculations of the
full distribution functions of the fringe contrast for the interference of
either the coherent or the number states of atoms. Another mechanism of the
suppression of the amplitude of interference fringes discussed in these lecture
notes is the quantum and thermal fluctuations of the order parameter in low
dimensional condensates. We summarize recent theoretical and experimental
studies demonstrating that suppression of the interference fringe contrast and
its shot to shot variations can be used to study correlation functions within
individual condensates. We also discuss full distribution functions of the
fringe amplitudes for one and two dimensional condensates and review their
connection to high order correlation functions. We point out intriguing
mathematical connections between the distribution functions of interference
fringe amplitudes and several other problems in field theory, systems of
correlated electrons, and statistical physics.; Comment: 47 pages...

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## Singlet-triplet splitting, correlation and entanglement of two electrons in quantum dot molecules

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

55.5%

Starting with an accurate pseudopotential description of the single-particle
states, and following by configuration-interaction treatment of correlated
electrons in vertically coupled, self-assembled InAs/GaAs quantum
dot-molecules, we show how simpler, popularly-practiced approximations, depict
the basic physical characteristics including the singlet-triplet splitting,
degree of entanglement (DOE) and correlation. The mean-field-like
single-configuration approaches such as Hartree-Fock and local spin density,
lacking correlation, incorrectly identify the ground state symmetry and give
inaccurate values for the singlet-triplet splitting and the DOE. The Hubbard
model gives qualitatively correct results for the ground state symmetry and
singlet-triplet splitting, but produces significant errors in the DOE because
it ignores the fact that the strain is asymmetric even if the dots within a
molecule are identical. Finally, the Heisenberg model gives qualitatively
correct ground state symmetry and singlet-triplet splitting only for rather
large inter-dot separations, but it greatly overestimates the DOE as a
consequence of ignoring the electron double occupancy effect.; Comment: 13 pages, 9 figures. To appear in Phys. Rev. B

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## Composite fermion theory of correlated electrons in semiconductor quantum dots in high magnetic fields

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/04/2004

Relevância na Pesquisa

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Interacting electrons in a semiconductor quantum dot at strong magnetic
fields exhibit a rich set of states, including correlated quantum fluids and
crystallites of various symmetries. We develop in this paper a perturbative
scheme based on the correlated basis functions of the composite-fermion theory,
that allows a systematic improvement of the wave functions and the energies for
low-lying eigenstates. For a test of the method, we study systems for which
exact results are known, and find that practically exact answers are obtained
for the ground state wave function, ground state energy, excitation gap, and
the pair correlation function. We show how the perturbative scheme helps
resolve the subtle physics of competing orders in certain anomalous cases.; Comment: 4 pages, 3 figures, 3 tables

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