2,171 research outputs found
Shadow band in the one-dimensional large Hubbard model
We show that the factorized wave-function of Ogata and Shiba can be used to
calculate the dependent spectral functions of the one-dimensional, infinite
Hubbard model, and of some extensions to finite . The resulting spectral
function is remarkably rich: In addition to low energy features typical of
Luttinger liquids, there is a well defined band, which we identify as the
shadow band resulting from spin fluctuations. This band should be
detectable experimentally because its intensity is comparable to that of the
main band for a large range of momenta.Comment: Latex file. 4 pages. Figures upon reques
Spectroscopic signatures of spin-charge separation in the quasi-one-dimensional organic conductor TTF-TCNQ
The electronic structure of the quasi-one-dimensional organic conductor
TTF-TCNQ is studied by angle-resolved photoelectron spectroscopy (ARPES). The
experimental spectra reveal significant discrepancies to band theory. We
demonstrate that the measured dispersions can be consistently mapped onto the
one-dimensional Hubbard model at finite doping. This interpretation is further
supported by a remarkable transfer of spectral weight as function of
temperature. The ARPES data thus show spectroscopic signatures of spin-charge
separation on an energy scale of the conduction band width.Comment: 4 pages, 4 figures; to appear in PR
Charge gap in the one--dimensional dimerized Hubbard model at quarter-filling
We propose a quantitative estimate of the charge gap that opens in the
one-dimensional dimerized Hubbard model at quarter-filling due to dimerization,
which makes the system effectively half--filled, and to repulsion, which
induces umklapp scattering processes. Our estimate is expected to be valid for
any value of the repulsion and of the parameter describing the dimerization. It
is based on analytical results obtained in various limits (weak coupling,
strong coupling, large dimerization) and on numerical results obtained by exact
diagonalization of small clusters. We consider two models of dimerization:
alternating hopping integrals and alternating on--site energies. The former
should be appropriate for the Bechgaard salts, the latter for compounds where
the stacks are made of alternating and molecules. % and ( denotes , , ...).Comment: 33 pages, RevTeX 3.0, figures on reques
Deducing correlation parameters from optical conductivity in the Bechgaard salts
Numerical calculations of the kinetic energy of various extensions of the
one-dimensional Hubbard model including dimerization and repulsion between
nearest neighbours are reported. Using the sum rule that relates the kinetic
energy to the integral of the optical conductivity, one can determine which
parameters are consistent with the reduction of the infrared oscillator
strength that has been observed in the Bechgaard salts. This leads to improved
estimates of the correlation parameters for both the TMTSF and TMTTF series.Comment: 12 pages, latex, figures available from the author
One particle interchain hopping in coupled Hubbard chains
Interchain hopping in systems of coupled chains of correlated electrons is
investigated by exact diagonalizations and Quantum-Monte-Carlo methods. For two
weakly coupled Hubbard chains at commensurate densities (e.g. n=1/3) the
splitting at the Fermi level between bonding and antibonding bands is strongly
reduced (but not suppressed) by repulsive interactions extending to a few
lattice spacings. The magnitude of this reduction is directly connected to the
exponent of the 1D Luttinger liquid. However, we show that the
incoherent part of the single particle spectral function is much less affected
by the interchain coupling. This suggests that incoherent interchain hopping
could occur for intermediate values.Comment: 4 pages, LaTeX 3.0, 7 PostScript figures in uuencoded for
Shadow features and shadow bands in the paramagnetic state of cuprate superconductors
The conditions for the precursors of antiferromagnetic bands in cuprate
superconductors are studied using weak-to-intermediate coupling approach. It is
shown that there are, in fact, three different precursor effects due to the
proximity to antiferromagnetic instability: i) the shadow band which associated
with new pole in the Green's function ii) the dispersive shadow feature due to
the thermal enhancement of the scattering rate and iii) the non-dispersive
shadow feature due to quantum spin fluctuation that exist only in
scan of the spectral function . I found
that dispersive shadow peaks in can exist at finite
temperature T in the renormalized classical regime, when ,
( is the characteristic energy of
spin fluctuations, is the thermal wave length of electron). In
contrast at zero temperature, only non-dispersive shadow feature in has been found. I found, however, that the latter
effect is always very small. The theory predict no shadow effects in the
optimally doped materials. The conditions for which shadow peaks can be
observed in photoemission are discussed.Comment: 6 pages, REVTEX, 2 ps figures, version to be published in PR
Spectral function of the 1D Hubbard model in the limit
We show that the one-particle spectral functions of the one-dimensional
Hubbard model diverge at the Fermi energy like
in the limit. The Luttinger liquid behaviour
, where as ,
should be limited to (for large but
finite), which shrinks to a single point, ,in that limit.
The consequences for the observation of the Luttinger liquid behaviour in
photoemission and inverse photoemission experiments are discussed.Comment: 4 pages, RevTeX, 2 figures on reques
Charge Ordering in the One-Dimensional Extended Hubbard Model: Implication to the TMTTF Family of Organic Conductors
We study the charge ordering (CO) in the one-dimensional (1D) extended
Hubbard model at quarter filling where the nearest-neighbor Coulomb repulsion
and dimerization in the hopping parameters are included. Using the cluster
mean-field approximation to take into account the effect of quantum
fluctuations, we determine the CO phase boundary of the model in the parameter
space at T=0 K. We thus find that the dimerization suppresses the stability of
the CO phase strongly, and in consequence, the realistic parameter values for
quasi-1D organic materials such as (TMTTF)PF are outside the region of
CO. We suggest that the long-range Coulomb interaction between the chains
should persist to stabilize the CO phase.Comment: 5 pages, 4 eps figures, to appear in 15 Nov. 2001 issue of PR
- …