64 research outputs found
Charge-Density-Wave Formation in the Doped Two-Leg Extended Hubbard Ladder
We investigate electronic properties of the doped two-leg Hubbard ladder with
both the onsite and the nearest-neighbor Coulomb repulsions, by using the the
weak-coupling renormalization-group method. It is shown that, for strong
nearest-neighbor repulsions, the charge-density-wave state coexisting with the
p-density-wave state becomes dominant fluctuation where spins form intrachain
singlets. By increasing doping rate, we have also shown that the effects of the
nearest-neighbor repulsions are reduced and the system exhibits a quantum phase
transition into the d-wave-like (or rung-singlet) superconducting state. We
derive the effective fermion theory which describes the critical properties of
the transition point with the gapless excitation of magnon. The phase diagram
of the two-leg ladder compound, Sr_{14-x}Ca_xCu_{24}O_{41}, is discussed.Comment: 4 pages, 2 figure
Interchain-Frustration-Induced Metallic State in Quasi-One-Dimensional Mott Insulators
The mechanism that drives a metal-insulator transition in an undoped
quasi-one-dimensional Mott insulator is examined in the framework of the
Hubbard model with two different hoppings t_{perp 1} and t_{perp 2} between
nearest-neighbor chains. By applying an N_{perp}-chain renormalization group
method at the two-loop level, we show how a metallic state emerges when both
t_{perp 1} and t_{perp 2} exceed critical values. In the metallic phase, the
quasiparticle weight becomes finite and develops a strong momentum dependence.
We discuss the temperature dependence of the resistivity and the impact of our
theory in the understanding of recent experiments on half-filled molecular
conductors.Comment: 4 pages, 3 figures, published versio
Magnetic response and quantum critical behavior in the doped two-leg extended Hubbard ladder
We have investigated quantum critical behavior in the doped two-leg extended
Hubbard ladder, by using a weak-coupling bosonization method. In the ground
state, the dominant fluctuation changes from the conventional d-wave-like
superconducting (SCd) state into density-wave states, with increasing
nearest-neighbor repulsions and/or decreasing doping rate. The competition
between the SCd state and the charge-density-wave state coexisting with the
p-density-wave state becomes noticeable on the critical point, at which the gap
for magnetic excitations vanishes. Based on the Majorana-fermion description of
the effective theory, we calculate the temperature dependence of the magnetic
response such as the spin susceptibility and the NMR relaxation rate, which
exhibit unusual properties due to two kinds of spin excitation modes. On the
quantum critical point, the spin susceptibility shows paramagnetic behavior
with logarithmic corrections and the NMR relaxation rate also exhibits
anomalous power-law behavior. We discuss the commensurability effect due to the
umklapp scattering and relevance to the two-leg ladder compounds
Sr_{14-x}Ca_xCu_{24}O_{41}.Comment: 18 pages, 9 figures, accepted for publication in Phys. Rev.
Competition of Dimerization and Charge Ordering in the Spin-Peierls State of Organic Conductors
The effect of the charge ordering on the spin-Peierls (SP) state has been
examined by using a Peierls-Hubbard model at quarter-filling with dimerization,
on-site and nearest-neighbor repulsive interactions. By taking account of the
presence of dimerization, a bond distortion is calculated variationally with
the renormalization group method based on bosonization. When the charge
ordering appears at V=V_c with increasing the nearest-neighbor interaction (V),
the distortion exhibits a maximum due to competition between the dimerization
and the charge ordering. It is shown that the second-order phase transition
occurs from the SP state with the bond alternation to a mixed state with an
additional component of the site alternationat V = V_c.Comment: 11 pages, 13 figures, to be published in J. Phys. Soc. Jpn. 72 No.6
(2003
Correlation function for the one-dimensional extended Hubbard model at quarter filling
We examine the density-density correlation function in the Tomonaga-Luttinger
liquid state for the one-dimensional extended Hubbard model with the on-site
Coulomb repulsion and the intersite repulsion at quarter filling. By
taking into account the effect of the marginally irrelevant umklapp scattering
operator by utilizing the renormalization-group technique based on the
bosonization method, we obtain the generalized analytical form of the
correlation function. We show that, in the proximity to the gapped
charge-ordered phase, the correlation function exhibits anomalous crossover
between the pure power-law behavior and the power-law behavior with logarithmic
corrections, depending on the length scale. Such a crossover is also confirmed
by the highly-accurate numerical density-matrix renormalization group method.Comment: 6 pages, 3 figure
Confinement-deconfinement transition in two-coupled chains with umklapp scattering
A role of umklapp scattering has been examined for two-coupled chains with
both forward and backward scatterings by applying renormalization group method
to bosonized Hamiltonian. It has been found that a state with relevant
interchain hopping changes into a state with irrelevant (confined) one when the
magnitude of umklapp scattering becomes larger than that of interchain hopping.
Critical value of umklapp scattering for such a confinement-deconfinement
transition is calculated as the function of interchain hopping and intrachain
interactions. A crossover from one-dimensional regime into that of coupled
chains is also shown with decreasing temperature.Comment: 13 pages, 7 figures, to be published in Phys. Rev.
Correlation Effect on Peierls Transition
The effect of correlation on Peierls transition, which is accompanied by a
dimerization, t_d, of a bond alternation for transfer energy, has been examined
for a half-filled one-dimensional electron system with on-site repulsive
interaction (U). By applying the renormalization group method to the
interaction of the bosonized Hamiltonian, the dimerization has been calculated
variationally and self-consistently with a fixed electron-phonon coupling
constant (\lambda) and it is shown that t_d takes a maximum as a function of U.
The result is examined in terms of charge gap and spin gap and is compared with
that of the numerical simulation by Hirsch [Phys. Rev. Lett 51 (1983) 296].
Relevance to the spin Peierls transition in organic conductors is discussed.Comment: 4 pages, 4 figures, to be published in J. Phys. Soc. Jpn. 71 No.3
(2002
Crossover from Quarter-Filling to Half-Filling in a One-Dimensional Electron System with a Dimerized and Quarter-Filled Band
The interplay between quarter-filled and half-filled umklapp scattering has
been examined by applying the renormalization group method to a one-dimensional
quarter-filled electron system with dimerization, on-site (U) and
nearest-neighbor (V) repulsive interactions. The phase diagram on the U-V plane
is obtained at absolute zero temperature where the Mott insulator (the charge
ordered insulator) is found for smaller (larger) V. By choosing the moderate
parameter in the region of Mott insulator, it is shown that the resistivity
exhibits a crossover from behavior of quarter-filling to that of half-filling
with decreasing temperature.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp
Two-loop renormalization-group theory for the quasi-one-dimensional Hubbard model at half filling
We derive two-loop renormalization-group equations for the half-filled
one-dimensional Hubbard chains coupled by the interchain hopping. Our
renormalization-group scheme for the quasi-one-dimensional electron system is a
natural extension of that for the purely one-dimensional systems in the sense
that transverse-momentum dependences are introduced in the g-ological coupling
constants and we regard the transverse momentum as a patch index. We develop
symmetry arguments for the particle-hole symmetric half-filled Hubbard model
and obtain constraints on the g-ological coupling constants by which resultant
renormalization equations are given in a compact form. By solving the
renormalization-group equations numerically, we estimate the magnitude of
excitation gaps and clarify that the charge gap is suppressed due to the
interchain hopping but is always finite even for the relevant interchain
hopping. To show the validity of the present analysis, we also apply this to
the two-leg ladder system. By utilizing the field-theoretical bosonization and
fermionization method, we derive low-energy effective theory and analyze the
magnitude of all the excitation gaps in detail. It is shown that the low-energy
excitations in the two-leg Hubbard ladder have SO(3) x SO(3) x U(1) symmetry
when the interchain hopping exceeds the magnitude of the charge gap.Comment: 18 pages, 9 figures; Two appendices and one figure adde
Quasi-One-Dimensional Spin-Density-Wave States with Two Kinds of Periodic Potentials and a Interchain Misfit
Spin density wave (SDW) states of a quasi-one-dimensional system with an
incommensurate wave vector perpendicular to the chain have been studied in the
presence of two kinds of commensurate potentials, which originate in a
quarter-filled band and dimerization along the chain. In terms of a phase
variable of the SDW order parameter, we treat classically the two-dimensional
Hamiltonian, which includes both acoustic excitations with long wave length and
a vortex excitation with short wave length. A phase diagram on the plane of
temperature and chemical potential (where the latter corresponds to the
deviation of the transverse wave vector from the commensurate one) exhibits a
variety of states given by the commensurate SDW state without charge density,
the commensurate SDW state with charge density, the incommensurate SDW state
and the disordered state
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