181 research outputs found
Spectral function of the one-dimensional Hubbard model away from half filling
We calculate the photoemission spectral function of the one-dimensional
Hubbard model away from half filling using the dynamical density matrix
renormalization group method. An approach for calculating momentum-dependent
quantities in finite open chains is presented. Comparison with exact Bethe
Ansatz results demonstrates the unprecedented accuracy of our method. Our
results show that the photoemission spectrum of the quasi-one-dimensional
conductor TTF-TCNQ provides evidence for spin-charge separation on the scale of
the conduction band width.Comment: REVTEX, 4 pages including 4 EPS figures (changed); correct chemical
potential used to define excitation energies in figures and tex
Charge and spin Drude weight of the one-dimensional extended Hubbard model at quarter-filling
We calculate the charge and spin Drude weight of the one-dimensional extended
Hubbard model with on-site repulsion and nearest-neighbor repulsion at
quarter filling using the density-matrix renormalization group method combined
with a variational principle. Our numerical results for the Hubbard model (V=0)
agree with exact results obtained from the Bethe ansatz solution. We obtain the
contour map for both Drude weights in the -parameter space for repulsive
interactions. We find that the charge Drude weight is discontinuous across the
Kosterlitz-Thouless transition between the Luttinger liquid and the
charge-density-wave insulator, while the spin Drude weight varies smoothly and
remains finite in both phases. Our results can be generally understood using
bosonization and renormalization group results. The finite-size scaling of the
charge Drude weight is well fitted by a polynomial function of the inverse
system size in the metallic region. In the insulating region we find an
exponential decay of the finite-size corrections with the system size and a
universal relation between the charge gap and the correlation length
which controls this exponential decay.Comment: 10 pages, 9 figure
Optical excitations in a one-dimensional Mott insulator
The density-matrix renormalization-group (DMRG) method is used to investigate
optical excitations in the Mott insulating phase of a one-dimensional extended
Hubbard model. The linear optical conductivity is calculated using the
dynamical DMRG method and the nature of the lowest optically excited states is
investigated using a symmetrized DMRG approach. The numerical calculations
agree perfectly with field-theoretical predictions for a small Mott gap and
analytical results for a large Mott gap obtained with a strong-coupling
analysis. Is is shown that four types of optical excitations exist in this Mott
insulator: pairs of unbound charge excitations, excitons, excitonic strings,
and charge-density-wave (CDW) droplets. Each type of excitations dominates the
low-energy optical spectrum in some region of the interaction parameter space
and corresponds to distinct spectral features: a continuum starting at the Mott
gap (unbound charge excitations), a single peak or several isolated peaks below
the Mott gap (excitons and excitonic strings, respectively), and a continuum
below the Mott gap (CDW droplets).Comment: 12 pages (REVTEX 4), 12 figures (in 14 eps files), 1 tabl
Operation of graphene quantum Hall resistance standard in a cryogen-free table-top system
Ground state phases of the Half-Filled One-Dimensional Extended Hubbard Model
Using quantum Monte Carlo simulations, results of a strong-coupling
expansion, and Luttinger liquid theory, we determine quantitatively the ground
state phase diagram of the one-dimensional extended Hubbard model with on-site
and nearest-neighbor repulsions U and V. We show that spin frustration
stabilizes a bond-ordered (dimerized) state for U appr. V/2 up to U/t appr. 9,
where t is the nearest-neighbor hopping. The transition from the dimerized
state to the staggered charge-density-wave state for large V/U is continuous
for U up to appr. 5.5 and first-order for higher U.Comment: 4 pages, 4 figure
Low-energy local density of states of the 1D Hubbard model
We examine the local density of states (DOS) at low energies numerically and
analytically for the Hubbard model in one dimension. The eigenstates represent
separate spin and charge excitations with a remarkably rich structure of the
local DOS in space and energy. The results predict signatures of strongly
correlated excitations in the tunneling probability along finite quantum wires,
such as carbon nanotubes, atomic chains or semiconductor wires in scanning
tunneling spectroscopy (STS) experiments. However, the detailed signatures can
only be partly explained by standard Luttinger liquid theory. In particular, we
find that the effective boundary exponent can be negative in finite wires,
which leads to an increase of the local DOS near the edges in contrast to the
established behavior in the thermodynamic limit.Comment: 6 pages, 4 figures, more information can be found at
http://www.physik.uni-kl.de/eggert/papers/index.htm
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
Differences Between Hole and Electron Doping of a Two-Leg CuO Ladder
Here we report results of a density-matrix-renormalization-group (DMRG)
calculation of the charge, spin, and pairing properties of a two-leg CuO
Hubbard ladder. The outer oxygen atoms as well as the rung and leg oxygen atoms
are included along with near-neighbor and oxygen-hopping matrix elements. This
system allows us to study the effects of hole and electron doping on a system
which is a charge transfer insulator at a filling of one hole per Cu and
exhibits power law, d-wave-like pairing correlations when doped. In particular,
we focus on the differences between doping with holes or electrons.Comment: REVTEX 4, 10 pages, 13 figure
Peierls transition in the presence of finite-frequency phonons in the one-dimensional extended Peierls-Hubbard model at half-filling
We report quantum Monte Carlo (stochastic series expansion) results for the
transition from a Mott insulator to a dimerized Peierls insulating state in a
half-filled, 1D extended Hubbard model coupled to optical bond phonons. Using
electron-electron (e-e) interaction parameters corresponding approximately to
polyacetylene, we show that the Mott-Peierls transition occurs at a finite
value of the electron-phonon (e-ph) coupling. We discuss several different
criteria for detecting the transition and show that they give consistent
results. We calculate the critical e-ph coupling as a function of the bare
phonon frequency and also investigate the sensitivity of the critical coupling
to the strength of the e-e interaction. In the limit of strong e-e couplings,
we map the model to a spin-Peierls chain and compare the phase boundary with
previous results for the spin-Peierls transition. We point out effects of a
nonlinear spin-phonon coupling neglected in the mapping to the spin-Peierls
model.Comment: 7 pages, 5 figure
- …