584 research outputs found
Metal-insulator transition in the Edwards model
To understand how charge transport is affected by a background medium and
vice versa we study a two-channel transport model which captures this interplay
via a novel, effective fermion-boson coupling. By means of (dynamical) DMRG we
prove that this model exhibits a metal-insulator transition at half-filling,
where the metal typifies a repulsive Luttinger liquid and the insulator
constitutes a charge density wave. The quantum phase transition point is
determined consistently from the calculated photoemission spectra, the scaling
of the Luttinger liquid exponent, the charge excitation gap, and the
entanglement entropy.Comment: 4 pages, 3 figures, contributions to SCES 201
DMRG analysis of the SDW-CDW crossover region in the 1D half-filled Hubbard-Holstein model
In order to clarify the physics of the crossover from a spin-density-wave
(SDW) Mott insulator to a charge-density-wave (CDW) Peierls insulator in
one-dimensional (1D) systems, we investigate the Hubbard-Holstein Hamiltonian
at half filling within a density matrix renormalisation group (DMRG) approach.
Determining the spin and charge correlation exponents, the momentum
distribution function, and various excitation gaps, we confirm that an
intervening metallic phase expands the SDW-CDW transition in the weak-coupling
regime.Comment: revised versio
Random dispersion approximation for the Hubbard model
We use the Random Dispersion Approximation (RDA) to study the Mott-Hubbard
transition in the Hubbard model at half band filling. The RDA becomes exact for
the Hubbard model in infinite dimensions. We implement the RDA on finite chains
and employ the Lanczos exact diagonalization method in real space to calculate
the ground-state energy, the average double occupancy, the charge gap, the
momentum distribution, and the quasi-particle weight. We find a satisfactory
agreement with perturbative results in the weak- and strong-coupling limits. A
straightforward extrapolation of the RDA data for lattice results in
a continuous Mott-Hubbard transition at . We discuss the
significance of a possible signature of a coexistence region between insulating
and metallic ground states in the RDA that would correspond to the scenario of
a discontinuous Mott-Hubbard transition as found in numerical investigations of
the Dynamical Mean-Field Theory for the Hubbard model.Comment: 10 pages, 11 figure
Tomonaga-Luttinger parameters for doped Mott insulators
The Tomonaga--Luttinger parameter determines the critical behavior
in quasi one-dimensional correlated electron systems, e.g., the exponent
for the density of states near the Fermi energy. We use the numerical
density-matrix renormalization group method to calculate from the
slope of the density-density correlation function in momentum space at zero
wave vector. We check the accuracy of our new approach against exact results
for the Hubbard and XXZ Heisenberg models. We determine in the phase
diagram of the extended Hubbard model at quarter filling, , and
confirm the bosonization results on the critical
line and at infinitesimal doping of the
charge-density-wave (CDW) insulator for all interaction strengths. The doped
CDW insulator exhibits exponents only for small doping and strong
correlations.Comment: 7 pages, 4 figure
One-Dimensional Quantum Transport Affected by a Background Medium: Fluctuations versus Correlations
We analyze the spectral properties of a very general two-channel
fermion-boson transport model in the insulating and metallic regimes, and the
signatures of the metal-insulator quantum phase transition in between. To this
end we determine the single particle spectral function related to
angle-resolved photoemission spectroscopy, the momentum distribution function,
the Drude weight and the optical response by means of a dynamical (pseudo-site)
density-matrix renormalization group technique for the one-dimensional
half-filled band case. We show how the interplay of correlations and
fluctuations in the background medium controls the charge dynamics of the
system, which is a fundamental problem in a great variety of advanced
materials.Comment: 6 pages, 5 figures, final versio
Thermodynamics of the one-dimensional half-filled Hubbard model in the spin-disordered regime
We analyze the Thermodynamic Bethe Ansatz equations of the one-dimensional
half-filled Hubbard model in the "spin-disordered regime", which is
characterized by the temperature being much larger than the magnetic energy
scale but small compared to the Mott-Hubbard gap. In this regime the
thermodynamics of the Hubbard model can be thought of in terms of gapped
charged excitations with an effective dispersion and spin degrees of freedom
that only contribute entropically. In particular, the internal energy and the
effective dispersion become essentially independent of temperature. An
interpretation of this regime in terms of a putative interacting-electron
system at zero temperature leads to a metal-insulator transition at a finite
interaction strength above which the gap opens linearly. We relate these
observations to studies of the Mott-Hubbard transition in the limit of infinite
dimensions.Comment: 15 pages, 3 figure
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