79 research outputs found
Finite-size scaling of correlation functions in one-dimensional Anderson-Hubbard model
We study the one-dimensional Anderson-Hubbard model using the density-matrix
renormalization group method. The influence of disorder on the
Tomonaga-Luttinger liquid behavior is quantitatively discussed. Based on the
finite-size scaling analysis of density-density correlation functions, we find
the following results: i) the charge exponent is significantly reduced by
disorder at low filling and near half filling, ii) the localization length
decays as , where is the disorder strength,
independently of the on-site Coulomb interaction as well as band filling, and
iii) the localization length is strongly suppressed by the on-site Coulomb
interaction near half filling in association with the formation of the Mott
plateaus.Comment: 4 pages, 4 figure
Local density of states of the one-dimensional spinless fermion model
We investigate the local density of states of the one-dimensional half-filled
spinless fermion model with nearest-neighbor hopping t>0 and interaction V in
its Luttinger liquid phase -2t < V <= 2t. The bulk density of states and the
local density of states in open chains are calculated over the full band width
4t with an energy resolution <= 0.08t using the dynamical density-matrix
renormalization group (DDMRG) method. We also perform DDMRG simulations with a
resolution of 0.01t around the Fermi energy to reveal the power-law behaviour
predicted by the Luttinger liquid theory for bulk and boundary density of
states. The exponents are determined using a finite-size scaling analysis of
DDMRG data for lattices with up to 3200 sites. The results agree with the exact
exponents given by the Luttinger liquid theory combined with the Bethe Ansatz
solution. The crossover from boundary to bulk density of states is analyzed. We
have found that boundary effects can be seen in the local density of states at
all energies even far away from the chain edges
Correlation gap in the optical spectra of the two-dimensional organic metal (BEDT-TTF)_4[Ni(dto)_2]
Optical reflection measurements within the highly conducting (a,b)-plane of
the organic metal (BEDT-TTF)_4[Ni(dto)_2] reveal the gradual development of a
sharp feature at around 200 cm as the temperature is reduced below 150 K. Below
this frequency a narrow Drude-like response is observed which accounts for the
metallic behavior. Since de Haas-von Alphen oscillations at low temperatures
confirm band structure calculations of bands crossing the Fermi energy, we
assign the observed behavior to a two-dimensional metallic state in the
proximity of a correlation induced metal-insulator transition.Comment: 4 pages, 2 figure
Crossover from Quarter-Filling to Half-Filling in a One-Dimensional Electron System with a Dimerized and Quarter-Filled Band
The interplay between quarter-filled and half-filled umklapp scattering has
been examined by applying the renormalization group method to a one-dimensional
quarter-filled electron system with dimerization, on-site (U) and
nearest-neighbor (V) repulsive interactions. The phase diagram on the U-V plane
is obtained at absolute zero temperature where the Mott insulator (the charge
ordered insulator) is found for smaller (larger) V. By choosing the moderate
parameter in the region of Mott insulator, it is shown that the resistivity
exhibits a crossover from behavior of quarter-filling to that of half-filling
with decreasing temperature.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp
Spin-density-wave transition of (TMTSF)PF at high magnetic fields
The transverse magnetoresistance of the Bechgaard salt (TMTSF)PF has
been measured for various pressures, with the field up to 24 T parallel to the
lowest conductivity direction c. A quadratic behavior is observed in
the magnetic field dependence of the spin-density-wave (SDW) transition
temperature . With increasing pressure,
decreases and the coefficient of the quadratic term increases. These results
are consistent with the prediction of the mean-field theory based on the
nesting of the quasi one-dimensional Fermi surface. Using a mean field theory,
for the perfect nesting case is estimated as about 16 K. This
means that even at ambient pressure where is 12 K, the SDW
phase of (TMTSF)PF is substantially suppressed by the
two-dimensionality of the system.Comment: 11pages,6figures(EPS), accepted for publication in PR
Optical conductivity of one-dimensional Mott insulators
We calculate the optical conductivity of one-dimensional Mott insulators at
low energies using a field theory description. The square root singularity at
the optical gap, characteristic of band insulators, is generally absent and
appears only at the Luther-Emery point. We also show that only few particle
processes contribute significantly to the optical conductivity over a wide
range of frequencies and that the bare perturbative regime is recovered only at
very large energies. We discuss possible applications of our results to quasi
one-dimensional organic conductors.Comment: 4 pages, 3 figures results adde
Infrared conductivity of a one-dimensional charge-ordered state: quantum lattice effects
The optical properties of the charge-ordering () phase of the
one-dimensional (1D) half-filled spinless Holstein model are derived at zero
temperature within a well-known variational approach improved including
second-order lattice fluctuations. Within the phase, the static lattice
distortions give rise to the optical interband gap, that broadens as the
strength of the electron-phonon () interaction increases. The lattice
fluctuation effects induce a long subgap tail in the infrared conductivity and
a wide band above the gap energy. The first term is due to the multi-phonon
emission by the charge carriers, the second to the interband transitions
accompanied by the multi-phonon scattering. The results show a good agreement
with experimental spectra.Comment: 5 figure
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
Current bistability and hysteresis in strongly correlated quantum wires
Nonequilibrium transport properties are determined exactly for an
adiabatically connected single channel quantum wire containing one impurity.
Employing the Luttinger liquid model with interaction parameter , for very
strong interactions g\lapx 0.2, and sufficiently low temperatures, we find an
S-shaped current-voltage relation. The unstable branch with negative
differential conductance gives rise to current oscillations and hysteretic
effects. These non perturbative and non linear features appear only out of
equilibrium.Comment: 4 pages, 1 figur
Searching for the Slater Transition in the Pyrochlore CdOsO with Infrared Spectroscopy
Infrared reflectance measurements were made on the single crystal pyrochlore
CdOsO in order to examine the transformations of the
electronic structure and crystal lattice across the boundary of the metal
insulator transition at . All predicted IR active phonons are
observed in the conductivity over all temperatures and the oscillator strength
is found to be temperature independent. These results indicate that charge
ordering plays only a minor role in the MIT and that the transition is strictly
electronic in nature. The conductivity shows the clear opening of a gap with
. The gap opens continuously, with a temperature
dependence similar to that of BCS superconductors, and the gap edge having a
distinct dependence. All of these
observables support the suggestion of a Slater transition in CdOsO.Comment: 4 pages, 4 figure
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