481 research outputs found

### Effect of Thermal Fluctuation on Spectral Function for the Tomonaga-Luttinger Model

We examine the spectral function of the single electron Green function at
finite temperatures for the Tomonaga-Luttinger model which consists of the
mutual interaction with only the forward scattering. The spectral weight, which
is calculated as a function of the frequency with the fixed wave number, shows
that several peaks originating in the excitation spectra of charge and spin
fluctuations vary into a single peak by the increase of temperature.Comment: 10 pages, 6 eps figure

### Competition of disorder and interchain hopping in a two-chain Hubbard model

We study the interplay of Anderson localization and interaction in a two
chain Hubbard ladder allowing for arbitrary ratio of disorder strength to
interchain coupling. We obtain three different types of spin gapped localized
phases depending on the strength of disorder: a pinned $4k_F$ Charge Density
Wave (CDW) for weak disorder, a pinned $2k_F$
CDW$^\pi$ for intermediate disorder and two independently pinned single chain
$2k_F$ CDW for strong disorder.
Confinement of electrons can be obtained as a result of strong disorder or
strong attraction. We give the full phase diagram as a function of disorder,
interaction strength and interchain hopping. We also study the influence of
interchain hopping on localization length and show that localization is
enhanced by a small interchain hopping but suppressed by a large interchain
hopping.Comment: 12 pages, uses svjour and svepj macros, 8 EPS figure

### 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

### 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

### On the Mott glass in the one-dimensional half-filled charge density waves

We study the effect of impurity pinning on a one-dimensional half-filled
electron system, which is expressed in terms of a phase Hamiltonian with the
charge degree of freedom. Within the classical treatment, the pinned state is
examined numerically. The Mott glass, which has been pointed out by Orignac et
al. [Phys. Rev. Lett 83 (1999) 2378], appears in the intermediate region where
the impurity potential competes with the commensurate potential. Such a state
is verified by calculating the soliton formation energy, the local restoring
force around the pinned state and the optical conductivity.Comment: 13 pages, 5 figures, to be published in J. Phys. Soc. Jpn. 72 No.11
(2003

### Role of Phase Variables in Quarter-Filled Spin Density Wave States

Several kinds of spin density wave (SDW) states with both quarter-filled band
and dimerization are reexamined for a one-dimensional system with on-site,
nearest-neighbor and next-nearest-neighbor repulsive interactions, which has
been investigated by Kobayashi et al. (J. Phys. Soc. Jpn. 67 (1998) 1098).
Within the mean-field theory, the ground state and the response to the density
variation are calculated in terms of phase variables, $\theta$ and $\phi$,
where $\theta$ expresses the charge fluctuation of SDW and $\phi$ describes the
relative motion between density wave with up spin and that with down spin
respectively. It is shown that the exotic state of coexistence of 2k_F-SDW and
2k_F-charge density wave (CDW) is followed by 4k_F-SDW but not by 4k_F-CDW
where k_F denotes a Fermi wave vector. The harmonic potential with respect to
the variation of $\theta$ and/or $\phi$ disappears for the interactions, which
lead to the boundary between the pure 2k_F-SDW state and the corresponding
coexistent state.Comment: 9 pages, 15 figures, to be published in J. Phys. Soc. Jpn. 69 No.3
(2000) 79

### Quarter-filled spin density wave states with long-range Coulomb interaction

Spin density wave (SDW) states at quarter-filling, which coexist with charge
density wave (CDW) states, have been examined where the critical temperature is
calculated for an extended Hubbard model with long range repulsive
interactions. Within the mean-field theory, it is shown that the first order
transition occurs with decreasing temperature for interactions located around
the boundary between SDW state and CDW state.Comment: 4 pages, 5 figures, Proceedings of CREST International Workshop
(Nagoya, Japan, 24-26 January, 2000), 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

### Effect of nearest- and next-nearest neighbor interactions on the spin-wave velocity of one-dimensional quarter-filled spin-density-wave conductors

We study spin fluctuations in quarter-filled one-dimensional
spin-density-wave systems in presence of short-range Coulomb interactions. By
applying a path integral method, the spin-wave velocity is calculated as a
function of on-site (U), nearest (V) and next-nearest (V_2) neighbor-site
interactions. With increasing V or V_2, the pure spin-density-wave state
evolves into a state with coexisting spin- and charge-density waves. The
spin-wave velocity is reduced when several density waves coexist in the ground
state, and may even vanish at large V. The effect of dimerization along the
chain is also considered.Comment: REVTeX, 11 pages, 9 figure

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