89 research outputs found
Mechanism of confinement in low-dimensional organic conductors
Confinement-deconfinement transition in quarter-filled two-coupled chains
comprising dimerization, repulsive interactions and interchain hopping has been
demonstrated by applying the renormalization group method to the bosonized
Hamiltonian. The confinement given by the irrelevant interchain hopping occurs
with increasing umklapp scattering which is induced by the dimerization leading
to effectively half-filling. It is shown that the transition originates in a
competition between a charge gap and the renormalized interchain hopping.Comment: 5 pages, 7 figures, Proc. CREST Int. Workshop, Nagoya 2000, submitted
to J. Phys. Chem. Solid
Generalized two-leg Hubbard ladder at half-filling: Phase diagram and quantum criticalities
The ground-state phase diagram of the half-filled two-leg Hubbard ladder with
inter-site Coulomb repulsions and exchange coupling is studied by using the
strong-coupling perturbation theory and the weak-coupling bosonization method.
Considered here as possible ground states of the ladder model are four types of
density-wave states with different angular momentum (s-density-wave state,
p-density-wave state, d-density-wave state, and f-density-wave state) and four
types of quantum disordered states, i.e., Mott insulating states (S-Mott,
D-Mott, S'-Mott, and D'-Mott states, where S and D stand for s- and d-wave
symmetry). The s-density-wave state, the d-density-wave state, and the D-Mott
state are also known as the charge-density-wave (CDW) state, the staggered-flux
(SF) state, and the rung-singlet state, respectively. Strong-coupling approach
naturally leads to the Ising model in a transverse field as an effective theory
for the quantum phase transitions between the SF state and the D-Mott state and
between the CDW state and the S-Mott state, where the Ising ordered states
correspond to doubly degenerate ground states in the staggered-flux or the
charge-density-wave state. From the weak-coupling bosonization approach it is
shown that there are three cases in the quantum phase transitions between a
density-wave state and a Mott state: the Ising (Z_2) criticality, the SU(2)_2
criticality, and a first-order transition. The quantum phase transitions
between Mott states and between density-wave states are found to be the U(1)
Gaussian criticality. The ground-state phase diagram is determined by
integrating perturbative renormalization-group equations. It is shown that the
S-Mott state and the SF state exist in the region sandwiched by the CDW phase
and the D-Mott phase.Comment: 21 pages, 10 figure
Competition of superfluidity and density waves in one-dimensional Bose-Fermi mixtures
We study a mixture of one-dimensional bosons and spinless fermions at
incommensurate filling using phenomenological bosonization and Green's
functions techniques. We derive the relation between the parameters of the
microscopic Hamiltonian and macroscopic observables. Galilean invariance
results in extra constraints for the current current interactions. We obtain
the exact exponents for the various response functions, and show that
superfluid fluctuations are enhanced by the effective boson-fermion
density-density interaction and suppressed by the effective boson-fermion
current-current interaction. In the case of a bosonized model with purely
density-density interaction, when the effective boson-fermion density-density
interaction is weak enough, the superfluid exponent of the bosons has a
non-monotonous variation with the ratio of the fermion velocity to the boson
velocity. By contrast, density-wave exponent and the exponent for fermionic
superfluidity are monotonous functions of the velocity ratio.Comment: 9 pages, RevTeX 4, 1 EPS figur
Combined Analysis of Numerical Diagonalization and Renormalization Group methods for the One-Dimensional - Model at Quarter filling
The one-dimensional extended Hubbard model with both the on-site and the
nearest neighbor interactions at quarter filling is studied by using a
novel finite size scaling. We diagonalize finite size systems numerically and
calculate the Luttinger-liquid parameter which is substituted into
the renormalization group equation as an initial condition. It leads
in the infinite size system and the result agrees very well with the available
exact result with . This approach also yields the charge gap in the
insulating state near the metal-insulator transition where the characteristic
energy becomes exponentially small and the usual finite size scaling is not
applicable.Comment: 7 pages, 8 figures,submitted to PR
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
Ising transition in a one-dimensional quarter-filled electron system with dimerization
We examine critical properties of the quarter-filled one-dimensional Hubbard
model with dimerization and with the onsite and nearest-neighbor Coulomb
repulsion U and V. By utilizing the bosonization method, it is shown that the
system exhibits an Ising quantum phase transition from the Mott insulating
state to the charge-ordered insulating state. It is also shown that the
dielectric permittivity exhibits a strong enhancement as decreasing temperature
with power-law dependence at the Ising critical point.Comment: 8 pages, 1 figure, uses elsart.cls, Proc. Int. Symp. ISSP-Kashiwa
2001, submitted to J. Phys. Chem. Solid
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
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
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