1,968 research outputs found
Ground State Properties of the Doped 3-Leg t-J Ladder
Results for a doped 3-leg t-J ladder obtained using the density matrix
renormalization group are reported. At low hole doping, the holes form a dilute
gas with a uniform density. The momentum occupation of the odd band shows a
sharp decrease at a large value of k_F similar to the behavior of a lightly
doped t-J chain, while the even modes appear gapped. The spin-spin correlations
decay as a power law consistent with the absence of a spin gap, but the pair
field correlations are negligible. At larger doping we find evidence for a spin
gap and as x increases further we find 3-hole diagonal domain walls. In this
regime there are pair field correlations and the internal pair orbital has
d_x^2-y^2 - like symmetry. However, the pair field correlations appear to fall
exponentially at large distances.Comment: 14 pages, 11 postscript figure
On the Nagaoka polaron in the t-J model
It is widely believed that a single hole in the two (or three) dimensional
t-J model, for sufficiently small exchange coupling J, creates a ferromagnetic
bubble around itself, a finite J remnant of the ferromagnetic groundstate at
J=0 (the infinite U Hubbard model), first established by Nagaoka. We
investigate this phenomenon in two dimensions using the density matrix
renormalization group, for system sizes up to 9x9. We find that the polaron
forms for J/t<0.02-0.03 (a somewhat larger value than estimated previously).
Although finite-size effects appear large, our data seems consistent with the
expected 1.1(J/t)^{-1/4} variation of polarion radius. We also test the
Brinkman-Rice model of non-retracing paths in a Neel background, showing that
it is quite accurate, at larger J. Results are also presented in the case where
the
Heisenberg interaction is dropped (the t-J^z model). Finally we discuss a
"dressed polaron" picture in which the hole propagates freely inside a finite
region but makes only self-retracing excursions outside this region.Comment: 7 pages, 9 encapsulated figure
Falicov-Kimball model and the problem of electronic ferroelectricity
The density matrix renormalization group method is used to examine
possibilities of electronic ferroelectricity in the spinless Falicov-Kimball
model. The model is studied for a wide range of parameters including weak and
strong interactions as well as the symmetric and unsymmetric case. In all
examined cases the -expectation value vanishes for vanishing
hybridization , indicating that the spinless Falicov-Kimball model does not
allow for a ferroelectric ground state with a spontaneous polarization.Comment: 9 pages, 4 figures, LaTe
The spin and charge gaps of the half-filled N-leg Kondo ladders
In this work, we study N-leg Kondo ladders at half-filling through the
density matrix renormalization group. We found non-zero spin and charge gaps
for any finite number of legs and Kondo coupling . We also show evidence
of the existence of a quantum critical point in the two dimensional Kondo
lattice model, in agreement with previous works. Based on the binding energy of
two holes, we did not find evidence of superconductivity in the 2D Kondo
lattice model close to half-filling.Comment: 4 pages, 1 table, 3 fig
Power laws in a 2-leg ladder of interacting spinless fermions
We use the Density-Matrix Renormalization Group to study the single-particle
and two-particle correlation functions of spinless fermions in the ground state
of a quarter-filled ladder. This ladder consists of two chains having an
in-chain extended Coulomb interaction reaching to third neighbor and coupled by
inter-chain hopping. Within our short numerical coherence lengths, typically
reaching ten to twenty sites, we find a strong renormalization of the
interchain hopping and the existence of a dimensional crossover at smaller
interactions. We also find power exponents for single-particle hopping and
interchain polarization consistent with the single chain. The total charge
correlation function has a larger power exponent and shows signs of a crossover
from incoherent fermion hopping to coherent particle-hole pair motion between
chains. There are no significant excitation energies.Comment: RevTex 4 file, 10 pages, 10 eps figure
Phase Transitions in the One-Dimensional Pair-Hopping Model: a Renormalization Group Study
The phase diagram of a one-dimensional tight-binding model with a
pair-hopping term (amplitude V) has been the subject of some controvery. Using
two-loop renormalization group equations and the density matrix renormalization
group with lengths L<=60, we argue that no spin-gap transition occurs at
half-filling for positive V, contrary to recent claims. However, we point out
that away from half-filling, a *phase-separation* transition occurs at finite
V. This transition and the spin-gap transition occuring at half-filling and
*negative* V are analyzed numerically.Comment: 7 pages RevTeX, 6 uuencoded figures which can be (and by default are)
directly included. Received by Phys. Rev. B 20 April 199
The Density Matrix Renormalization Group Method and Large-Scale Nuclear Shell-Model Calculations
The particle-hole Density Matrix Renormalization Group (p-h DMRG) method is
discussed as a possible new approach to large-scale nuclear shell-model
calculations. Following a general description of the method, we apply it to a
class of problems involving many identical nucleons constrained to move in a
single large j-shell and to interact via a pairing plus quadrupole interaction.
A single-particle term that splits the shell into degenerate doublets is
included so as to accommodate the physics of a Fermi surface in the problem. We
apply the p-h DMRG method to this test problem for two values, one for
which the shell model can be solved exactly and one for which the size of the
hamiltonian is much too large for exact treatment. In the former case, the
method is able to reproduce the exact results for the ground state energy, the
energies of low-lying excited states, and other observables with extreme
precision. In the latter case, the results exhibit rapid exponential
convergence, suggesting the great promise of this new methodology even for more
realistic nuclear systems. We also compare the results of the test calculation
with those from Hartree-Fock-Bogolyubov approximation and address several other
questions about the p-h DMRG method of relevance to its usefulness when
treating more realistic nuclear systems
Stripe orientation in an anisotropic t-J model
The tilt pattern of the CuO_6 octahedra in the LTT phase of the cuprate
superconductors leads to planar anisotropies for the exchange coupling and
hopping integrals. Here, we show that these anisotropies provide a possible
structural mechanism for the orientation of stripes. A t_x-t_y-J_x-J_y model
thus serves as an effective Hamiltonian to describe stripe formation and
orientation in LTT-phase cuprates.Comment: 3 pages, 3 figure
Operator-Based Truncation Scheme Based on the Many-Body Fermion Density Matrix
In [S. A. Cheong and C. L. Henley, cond-mat/0206196 (2002)], we found that
the many-particle eigenvalues and eigenstates of the many-body density matrix
of a block of sites cut out from an infinite chain of
noninteracting spinless fermions can all be constructed out of the one-particle
eigenvalues and one-particle eigenstates respectively. In this paper we
developed a statistical-mechanical analogy between the density matrix
eigenstates and the many-body states of a system of noninteracting fermions.
Each density matrix eigenstate corresponds to a particular set of occupation of
single-particle pseudo-energy levels, and the density matrix eigenstate with
the largest weight, having the structure of a Fermi sea ground state,
unambiguously defines a pseudo-Fermi level. We then outlined the main ideas
behind an operator-based truncation of the density matrix eigenstates, where
single-particle pseudo-energy levels far away from the pseudo-Fermi level are
removed as degrees of freedom. We report numerical evidence for scaling
behaviours in the single-particle pseudo-energy spectrum for different block
sizes and different filling fractions \nbar. With the aid of these
scaling relations, which tells us that the block size plays the role of an
inverse temperature in the statistical-mechanical description of the density
matrix eigenstates and eigenvalues, we looked into the performance of our
operator-based truncation scheme in minimizing the discarded density matrix
weight and the error in calculating the dispersion relation for elementary
excitations. This performance was compared against that of the traditional
density matrix-based truncation scheme, as well as against a operator-based
plane wave truncation scheme, and found to be very satisfactory.Comment: 22 pages in RevTeX4 format, 22 figures. Uses amsmath, amssymb,
graphicx and mathrsfs package
Unscreened Coulomb repulsion in the one dimensional electron gas
A tight binding model of electrons interacting via bare Coulomb repulsion is
numerically investigated by use of the Density Matrix Renormalization Group
method which we prove applicable also to very long range potentials. From the
analysis of the elementary excitations, of the spin and charge correlation
functions and of the momentum distribution, a picture consistent with the
formation of a one dimensional "Wigner crystal" emerges, in quantitative
agreement with a previous bosonization study. At finite doping, Umklapp
scattering is shown to be ineffective in the presence of long range forces.Comment: RevTex, 5 pages with 8 eps figures. To be published on Phys. Rev.
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