465 research outputs found
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
Phase diagram of the one-dimensional half-filled extended Hubbard model
We study the ground state of the one-dimensional half-filled Hubbard model
with on-site (nearest-neighbor) repulsive interaction () and
nearest-neighbor hopping . In order to obtain an accurate phase diagram, we
consider various physical quantities such as the charge gap, spin gap,
Luttinger-liquid exponents, and bond-order-wave (BOW) order parameter using the
density-matrix renormalization group technique. We confirm that the BOW phase
appears in a substantial region between the charge-density-wave (CDW) and
spin-density-wave phases. Each phase boundary is determined by multiple means
and it allows us to do a cross-check to demonstrate the validity of our
estimations. Thus, our results agree quantitatively with the renormalization
group results in the weak-coupling regime (), with the
perturbation results in the strong-coupling regime (), and with
the quantum Monte Carlo results in the intermediate-coupling regime. We also
find that the BOW-CDW transition changes from continuous to first order at the
tricritical point and the BOW
phase vanishes at the critical end point .Comment: 4 pages, 5 figure
Vaccination and clinical severity: Is the effectiveness of contact tracing and case isolation hampered by past vaccination?
published_or_final_versio
Peierls to superfluid crossover in the one-dimensional, quarter-filled Holstein model
We use continuous-time quantum Monte Carlo simulations to study retardation
effects in the metallic, quarter-filled Holstein model in one dimension. Based
on results which include the one- and two-particle spectral functions as well
as the optical conductivity, we conclude that with increasing phonon frequency
the ground state evolves from one with dominant diagonal order---2k_F charge
correlations---to one with dominant off-diagonal fluctuations, namely s-wave
pairing correlations. In the parameter range of this crossover, our numerical
results support the existence of a spin gap for all phonon frequencies. The
crossover can hence be interpreted in terms of preformed pairs corresponding to
bipolarons, which are essentially localised in the Peierls phase, and
"condense" with increasing phonon frequency to generate dominant pairing
correlations.Comment: 11 pages, 5 figure
Phase Diagram of the ------ Model at Quarter Filling
We examine the ground-state properties of the one-dimensional Hubbard model
at quarter filling with Coulomb interactions between nearest-neighbors
and next-nearest neighbors . Using the density-matrix renormalization
group and exact diagonalization methods, we obtain an accurate ground-state
phase diagram in the - plane with three different phases: - and -charge-density-wave and a broad metallic phase
in-between. The metal is a Tomonaga-Luttinger-liquid whose critical exponent
is largest around , where and are frustrated,
and smallest, , at the boundaries between the metallic phase and
each of the two ordered phases.Comment: 4 pages, 5 figures, sumitted to PR
Phase separation in the Edwards model
The nature of charge transport within a correlated background medium can be
described by spinless fermions coupled to bosons in the model introduced by
Edwards. Combining numerical density matrix renormalization group and
analytical projector-based renormalization methods we explore the ground-state
phase diagram of the Edwards model in one dimension. Below a critical boson
frequency any long-range order disappears and the system becomes metallic. If
the charge carriers are coupled to slow quantum bosons the Tomonaga-Luttinger
liquid is attractive and finally makes room for a phase separated state, just
as in the t-J model. The phase boundary separating repulsive from the
attractive Tomonaga-Luttinger liquid is determined from long-wavelength charge
correlations, whereas fermion segregation is indicated by a vanishing inverse
compressibility. On approaching phase separation the photoemission spectra
develop strong anomalies.Comment: 6 pages, 5 figures, final versio
- …