153 research outputs found
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
Competing effects of interactions and spin-orbit coupling in a quantum wire
We study the interplay of electron-electron interactions and Rashba
spin-orbit coupling in one-dimensional ballistic wires. Using the
renormalization group approach we construct the phase diagram in terms of
Rashba coupling, Tomonaga-Luttinger stiffness and backward scattering strength.
We identify the parameter regimes with a dynamically generated spin gap and
show where the Luttinger liquid prevails. We also discuss the consequences for
the operation of the Datta-Das transistor.Comment: 4 pages, 2 figure
Extended scaling behavior of the spatially-anisotropic classical XY model in the crossover from three to two dimensions
The bivariate high-temperature expansion of the spin-spin
correlation-function of the three-dimensional classical XY (planar rotator)
model, with spatially-anisotropic nearest-neighbor couplings, is extended from
the 10th through the 21st order. The computation is carried out for the
simple-cubic lattice, in the absence of magnetic field, in the case in which
the coupling strength along the z-axis of the lattice is different from those
along the x- and the y-axes. It is then possible to determine accurately the
critical temperature as function of the parameter R which characterizes the
coupling anisotropy and to check numerically the universality, with respect to
R, of the critical exponents of the three-dimensional anisotropic system. The
analysis of our data also shows that the main predictions of the generalized
scaling theory for the crossover from the three-dimensional to the
two-dimensional critical behavior are compatible with the series
extrapolations.Comment: 29 pages, 7 figure
Solution of the infinite range t-J model
The t-J model with constant t and J between any pair of sites is studied by
exploiting the symmetry of the Hamiltonian with respect to site permutations.
For a given number of electrons and a given total spin the exchange term simply
yields an additive constant. Therefore the real problem is to diagonalize the
"t- model", or equivalently the infinite U Hubbard Hamiltonian. Using
extensively the properties of the permutation group, we are able to find
explicitly both the energy eigenvalues and eigenstates, labeled according to
spin quantum numbers and Young diagrams. As a corollary we also obtain the
degenerate ground states of the finite Hubbard model with infinite range
hopping -t>0.Comment: 15 pages, 2 figure
Solitonic approach to the dimerization problem in correlated one-dimensional systems
Using exact diagonalizations we consider self-consistently the lattice
distortions in odd Peierls-Hubbard and spin-Peierls periodic rings in the
adiabatic harmonic approximation. From the tails of the inherent spin soliton
the dimerization d_\infty of regular even rings is found by extrapolations to
infinite ring lengths. Considering a wide region of electron-electron onsite
interaction values U>0 compared with the band width 4t_0 at intermediately
strong electron-phonon interaction g, known relationships obtained by other
methods are reproduced and/or refined within one unified approach: such as the
maximum of d_\infty at U \simeq 3 t_0 for g \simeq 0.5 and its shift to zero
for g \to g_c \approx 0.7. The hyperbolic tangent shape of the spin soliton is
retained for any U and g <~ 0.6. In the spin-Peierls limit the d_\infty are
found to be in agreement with results of DMRG computations.Comment: 4 pages, 4 figures, Physical Review B, Rapid Communications, v. 56
(1997) accepte
Temperature dependence of optical spectral weights in quarter-filled ladder systems
The temperature dependence of the integrated optical conductivity I(T)
reflects the changes of the kinetic energy as spin and charge correlations
develop. It provides a unique way to explore experimentally the kinetic
properties of strongly correlated systems. We calculated I(T) in the frame of a
t-J-V model at quarter-filling for ladder systems, like NaV_2O_5, and show that
the measured strong T dependence of I(T) for NaV_2O_5 can be explained by the
destruction of short range antiferromagnetic correlations. Thus I(T) provides
detailed information about super-exchange and magnetic energy scales.Comment: 4 pages, 5 figure
Low-temperature transport in Heisenberg chains
A technique to determine accurately transport properties of integrable and
non-integrable quantum-spin chains at finite temperatures by Quantum
Monte-Carlo is presented. The reduction of the Drude weight by interactions in
the integrable gapless regime is evaluated. Evidence for the absence of a Drude
weight in the gapless regime of a non-integrable system with longer-ranged
interactions is presented. We estimate the effect of the non-integrability on
the transport properties and compare with recent experiments on one-dimensional
quantum-spin chains.Comment: accepted for publication (PRL
Nonlinear Optical Response of Spin Density Wave Insulators
We calculate the third order nonlinear optical response in the Hubbard model
within the spin density wave (SDW) mean field ansatz in which the gap is due to
onsite Coulomb repulsion. We obtain closed-form analytical results in one
dimension (1D) and two dimension (2D), which show that nonlinear optical
response in SDW insulators in 2D is stronger than both 3D and 1D. We also
calculate the two photon absorption (TPA) arising from the stress tensor term.
We show that in the SDW, the contribution from stress tensor term to the
low-energy peak corresponding to two photon absorption becomes identically zero
if we consider the gauge invariant current properly.Comment: we use \psfrag in figur
On the correllation effect in Peierls-Hubbard chains
We reexamine the dimerization, the charge and the spin gaps of a half-filled
Peierls-Hubbard chain by means of the incremental expansion technique. Our
numerical findings are in significant quantitative conflict with recently
obtained results by M. Sugiura and Y. Suzumura [J. Phys. Soc. Jpn. v. 71 (2002)
697] based on a bosonization and a renormalization group method, especially
with respect to the charge gap. Their approach seems to be valid only in the
weakly correlated case.Comment: 7pages,4figures(6eps-files
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