237 research outputs found
Unified phase diagram of models exhibiting neutral-ionic transition
We have studied the neutral-ionic transition in organic mixed-stack
compounds. A unified model has been derived which, in limiting cases, is
equivalent to the models proposed earlier, the donor-acceptor model and the
ionic Hubbard model. Detailed numerical calculations have been performed on
this unified model with the help of the density-matrix renormalization-group
(DMRG) procedure calculating excitation gaps, ionicity, lattice site entropy,
two-site entropy, and the dimer order parameter on long chains and the unified
phase diagram has been determined.Comment: 11 pages, 8 figure
How to Play 3x3 Games: A Strategy Method Experiment
Using the strategy method (Selten 1967) we elicit subjects' strategies for playing any 2-person 3x3-game with integer payoffs between 0 and 99.In each of 5 tournaments, every strategy pair plays 500000 games.The frequency of pure strategy equilibrium play increases from 51% in the first to 74% in the last tournament, with the equilibria that maximize joint payoff being preferred when multiple exist.For games without pure equilibria, strategies are typically based on elements of the best-reply cascade: MAP (maximize the expected payoff against uniformly randomizing opponents), BR-MAP (best reply to MAP), and BR-BR-MAP (best reply to BR-MAP).game theory;experimental economics
Mott transition and dimerization in the one-dimensional SU Hubbard model
The one-dimensional SU Hubbard model is investigated numerically for
, and 5 at half filling and filling using the density-matrix
renormalization-group (DMRG) method. The energy gaps and various quantum
information entropies are calculated. In the half-filled case, finite spin and
charge gaps are found for arbitrary positive if . Furthermore, it is
shown that the transition to the gapped phase at is of
Kosterlitz-Thouless type and is accompanied by a bond dimerization both for
even and odd . In the -filled case, the transition has similar features
as the metal-insulator transition in the half-filled SU(2) Hubbard model. The
charge gap opens exponentially slowly for , the spin sector
remains gapless, and the ground state is non-dimerized.Comment: 9 pages, 12 figure
Probable absence of a quadrupolar spin-nematic phase in the bilinear-biquadratic spin-1 chain
We study numerically the ground-state phase diagram of the
bilinear-biquadratic spin-1 chain near the ferromagnetic instability point,
where the existence of a gapped or gapless nondimerized quantum nematic phase
has been suggested. Our results, obtained by a highly accurate density-matrix
renormalization-group (DMRG) calculation are consistent with the view that the
order parameter characterizing the dimer phase vanishes only at the point where
the system becomes ferromagnetic, although the existence of a gapped or gapless
nondimerized phase in a very narrow parameter range between the ferromagnetic
and the dimerized regimes cannot be ruled out.Comment: 6 pages, 6 figure
SU(N) quantum spin models: A variational wavefunction study
The study of SU(N) quantum spin models is relevant to a variety of physical
systems including ultracold atoms in optical lattices, and also leads to
insights into novel quantum phases and phase transitions of SU(2) spin models.
We use Gutzwiller projected fermionic variational wavefunctions to explore the
phase diagram and correlation functions of SU(N) spin models in the
self-conjugate representation, with Heisenberg bilinear and biquadratic
interactions. In 1D, the variational phase diagram of the SU(4) spin chain is
constructed by examining instabilities of the Gutzwiller projected free fermion
ground state to various broken symmetries, and it agrees well with exact
results.The spin and dimer correlations of the Gutzwiller projected free
fermion state with N flavors of fermions are also in good agreement with exact
and 1/N calculations for the critical points of SU(N) spin chains. In 2D, the
variational phase diagram on the square lattice is obtained by studying
instabilities of the Gutzwiller projected pi-flux state. The variational ground
state of the pure Heisenberg model is found to exhibit long range Neel order
for N=2,4 and spin Peierls order for N > 4. For N=4 and 6, biquadratic
interactions lead to a complex phase diagram which includes an extended valence
bond crystal in both cases, as well as a stable pi-flux phase for N=6. The spin
correlations of the projected pi-flux state at N=4 are in good agreement with
1/N calculations. We find that this state also shows strongly enhanced dimer
correlations, in qualitative accord with the large-N results. We compare our
results with a recent QMC study of the SU(4) Heisenberg model.Comment: 22 pages, 7 figs, added references to arxiv versio
EUV ionization of pure He nanodroplets: Mass-correlated photoelectron imaging, Penning ionization and electron energy-loss spectra
The ionization dynamics of pure He nanodroplets irradiated by EUV radiation
is studied using Velocity-Map Imaging PhotoElectron-PhotoIon COincidence
(VMI-PEPICO) spectroscopy. We present photoelectron energy spectra and angular
distributions measured in coincidence with the most abundant ions He+, He2+,
and He3+. Surprisingly, below the autoionization threshold of He droplets we
find indications for multiple excitation and subsequent ionization of the
droplets by a Penning-like process. At high photon energies we evidence
inelastic collisions of photoelectrons with the surrounding He atoms in the
droplets
Penning ionization of doped helium nanodroplets following EUV excitation
Helium nanodroplets are widely used as a cold, weakly interacting matrix for
spectroscopy of embedded species. In this work we excite or ionize doped He
droplets using synchrotron radiation and study the effect onto the dopant atoms
depending on their location inside the droplets (rare gases) or outside at the
droplet surface (alkali metals). Using photoelectron-photoion coincidence
imaging spectroscopy at variable photon energies (20-25 eV), we compare the
rates of charge-transfer to Penning ionization of the dopants in the two cases.
The surprising finding is that alkali metals, in contrast to the rare gases,
are efficiently Penning ionized upon excitation of the (n=2)-bands of the host
droplets. This indicates rapid migration of the excitation to the droplet
surface, followed by relaxation, and eventually energy transfer to the alkali
dopants
The evaluation of the impact of support on Lithuanian farms investments
Straipsnio tikslas – įvertinti paramos poveikį Lietuvos ūkių investicijoms. Tyrimo metu buvo sudarytas logit modelis, įgalinantis nustatyti ūkininkų tikimybę investuoti. Tyrimui buvo naudoti 2013 metų Lietuvos ūkininkų, įtrauktų į Ūkių apskaitos duomenų tinklą (ŪADT), duomenys. Vertintos investicijos į žemės ūkio mašinas ir įrenginius. Remiantis tyrimu nustatyta, kad parama skatina ūkių investicijas, tačiau scenarijų analizės metu nustatyta, kad jos pokyčiai tikimybę investuoti veikia nedaug. Taip pat tyrimu atskleista, kad ūkių investicijoms daug įtakos turi ūkio charakteristikos.The paper aims to evaluate the impact of support on Lithuanian farms investments. Logistic regression, also called a logit model, was used to determine the probability of investing. The regression was estimated on cross-sectional data set of Lithuanian family farms participating in the Farm Accountancy Data Network. It was specified for investments in machinery and equipment. The research showed that support encourages investments in machinery and equipment. However, scenario analysis revealed that the impact of different support scenarios on the probability of investing is relatively small. It was also confirmed the importance of farm characteristics in making investments
Insulating charge density wave for a half-filled SU(N) Hubbard model with an attractive on-site interaction in one dimension
We study a one-dimensional SU(N) Hubbard model with an attractive on-site
interaction and at half-filling on the bipartite lattice using
density-matrix renormalization-group method and a perturbation theory. We find
that the ground state of the SU(N) Hubbard model is a charge density wave state
with two-fold degeneracy. All the excitations are found to be gapful, resulting
in an insulating ground state, on contrary to that in the SU(2) case. Moreover,
the charge gap is equal to the Cooperon gap, which behaves as
in the strong coupling regime. However, the spin gap and the
quasiparticle gap as well open exponentially in the weak coupling
region, while in the strong coupling region, they linearly depend on such
that and .Comment: 7 pages, 7 figure
Quantum Non-Demolition Detection of Strongly Correlated Systems
Preparation, manipulation, and detection of strongly correlated states of
quantum many body systems are among the most important goals and challenges of
modern physics. Ultracold atoms offer an unprecedented playground for
realization of these goals. Here we show how strongly correlated states of
ultracold atoms can be detected in a quantum non-demolition scheme, that is, in
the fundamentally least destructive way permitted by quantum mechanics. In our
method, spatially resolved components of atomic spins couple to quantum
polarization degrees of freedom of light. In this way quantum correlations of
matter are faithfully mapped on those of light; the latter can then be
efficiently measured using homodyne detection. We illustrate the power of such
spatially resolved quantum noise limited polarization measurement by applying
it to detect various standard and "exotic" types of antiferromagnetic order in
lattice systems and by indicating the feasibility of detection of superfluid
order in Fermi liquids.Comment: Published versio
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