802 research outputs found
The Structure of the Pairing Interaction in the 2D Hubbard Model
Dynamic cluster Monte Carlo calculations for the doped two-dimensional
Hubbard model are used to study the irreducible particle-particle vertex
responsible for pairing in this model. This vertex increases with
increasing momentum transfer and decreases when the energy transfer exceeds a
scale associated with the spin susceptibility. Using an exact
decomposition of this vertex into a fully irreducible two-fermion vertex and
charge and magnetic exchange channels, the dominant part of the effective
pairing interaction is found to come from the magnetic, spin S=1 exchange
channel.Comment: Published version. 4 pages, 4 figure
Systematic analysis of a spin-susceptibility representation of the pairing interaction in the 2D Hubbard model
A dynamic cluster quantum Monte Carlo algorithm is used to study a spin
susceptibility representation of the pairing interaction for the
two-dimensional Hubbard model with an on-site Coulomb interaction equal to the
bandwidth for various doping levels. We find that the pairing interaction is
well approximated by {3/2}\Ub(T)^2\chi(K-K') with an effective temperature
and doping dependent coupling \Ub(T) and the numerically calculated spin
susceptibility . We show that at low temperatures, \Ub may be
accurately determined from a corresponding spin susceptibility based
calculation of the single-particle self-energy. We conclude that the strength
of the d-wave pairing interaction, characterized by the mean-field transition
temperature, can be determined from a knowledge of the dressed spin
susceptibility and the nodal quasiparticle spectral weight. This has important
implications with respect to the questions of whether spin fluctuations are
responsible for pairing in the high-T cuprates.Comment: 5 pages, 5 figure
Spin Susceptibility Representation of the Pairing Interaction for the two-dimensional Hubbard Model
Using numerical dynamic cluster quantum Monte Carlo results, we study a
simple approximation for the pairing interaction of a two-dimensional Hubbard
model with an on-site Coulomb interaction equal to the bandwidth. We find
that with an effective temperature dependent coupling \Ub(T) and the
numerically calculated spin susceptibility , the d-wave pairing
interaction is well approximated by \frac{3}{2} \Ub^2\chi(K-K').Comment: 5 pages, 7 figure
Phase Stability in the Two dimensional Anisotropic Boson Hubbard Hamiltonian
The two dimensional square lattice hard-core boson Hubbard model with near
neighbor interactions has a `checkerboard' charge density wave insulating phase
at half-filling and sufficiently large intersite repulsion. When doped, rather
than forming a supersolid phase in which long range charge density wave
correlations coexist with a condensation of superfluid defects, the system
instead phase separates. However, it is known that there are other lattice
geometries and interaction patterns for which such coexistence takes place. In
this paper we explore the possibility that anisotropic hopping or anisotropic
near neighbor repulsion might similarly stabilize the square lattice
supersolid. By considering the charge density wave structure factor and
superfluid density for different ratios of interaction strength and
hybridization in the and directions, we conclude that phase
separation still occurs.Comment: 8 pages, 11 figure
Temperature-dependent electronic structure and ferromagnetism in the d=oo Hubbard model studied by a modfied perturbation theory
The infinite-dimensional Hubbard model is studied by means of a modified
perturbation theory. The approach reduces to the iterative perturbation theory
for weak coupling. It is exact in the atomic limit and correctly reproduces the
dispersions and the weights of the Hubbard bands in the strong-coupling regime
for arbitrary fillings. Results are presented for the hyper-cubic and an
fcc-type lattice. For the latter we find ferromagnetic solutions. The
filling-dependent Curie temperature is compared with the results of a recent
Quantum Monte Carlo study.Comment: RevTeX, 5 pages, 6 eps figures included, Phys. Rev. B (in press),
Ref. 16 correcte
Thermoelectric Response Near the Density Driven Mott Transition
We investigate the thermoelectric response of correlated electron systems
near the density driven Mott transition using the dynamical mean field theory.Comment: 4 pages, 2 embedded figure
ARPES Spectra of the Hubbard model
We discuss spectra calculated for the 2D Hubbard model in the intermediate
coupling regime with the dynamical cluster approximation, which is a
non-perturbative approach. We find a crossover from a normal Fermi liquid with
a Fermi surface closed around the Brillouin zone center at large doping to a
non-Fermi liquid for small doping. The crossover is signalled by a splitting of
the Fermi surface around the point of the 2D Brillouin zone, which
eventually leads to a hole-like Fermi surface closed around the point M. The
topology of the Fermi surface at low doping indicates a violation of
Luttinger's theorem. We discuss different ways of presenting the spectral data
to extract information about the Fermi surface. A comparison to recent
experiments will be presented.Comment: 8 pages, 7 color figures, uses RevTeX
Absence of hysteresis at the Mott-Hubbard metal-insulator transition in infinite dimensions
The nature of the Mott-Hubbard metal-insulator transition in the
infinite-dimensional Hubbard model is investigated by Quantum Monte Carlo
simulations down to temperature T=W/140 (W=bandwidth). Calculating with
significantly higher precision than in previous work, we show that the
hysteresis below T_{IPT}\simeq 0.022W, reported in earlier studies, disappears.
Hence the transition is found to be continuous rather than discontinuous down
to at least T=0.325T_{IPT}. We also study the changes in the density of states
across the transition, which illustrate that the Fermi liquid breaks down
before the gap opens.Comment: 4 pages, 4 eps-figures using epsf.st
Stabilization of d-Band Ferromagnetism by Hybridization with Uncorrelated Bands
We investigate the influence of s-d or p-d hybridization to d-band
ferromagnetism to estimate the importance of hybridization for the magnetic
properties of transition metals. To focus our attention to the interplay
between hybridization and correlation we investigate a simple model system
consisting of two non-degenerated hybridized bands, one strongly correlated,
the other one quasi-free. To solve this extended Hubbard model, we apply simple
approximations, namely SDA and MAA, that, concerning ferromagnetism in the
single-band model, are known to give qualitatively satisfactory results. This
approach allows us to discuss the underlying mechanism, by which d-band
ferromagnetism is influenced by the hybridization on the basis of analytical
expressions. The latter clearly display the order and the functional
dependencies of the important effects. It is found, that spin-dependent
inter-band particle fluctuations cause a spin-dependent band shift and a
spin-dependent band broadening of the Hubbard bands. The shift stabilizes, the
broadening tends to destabilize ferromagnetism. Stabilization requires
relatively high band distances and small hybridization matrix elements.
Super-exchange and RKKY coupling are of minor importance.Comment: 9 pages, 7 figures, accepted for PR
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