657 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
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, and ,
where expresses the charge fluctuation of SDW and 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 and/or 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
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
N\'eel and singlet RVB orders in the t-J model
The N\'eel and the singlet RVB orders of the {\it t-J} model in a 2D square
lattice are studied in the slave-boson mean-field approximation. It is shown
that the N\'eel order parameter takes the maximum value at the finite
temperature and disappear at the lower temperature for a certain range of
doping. It is also shown that the N\'eel and the singlet RVB orders coexist at
low temperature. This suggests the possibility of the coexistence of the N\'eel
and the superconducting orders.Comment: RevTeX, 8 pages, 1 postscript figure. To appear in Physica C, Volume
257, issue 38
Exact-Differential Large-Scale Traffic Simulation
Analyzing large-scale traffics by simulation needs repeating execution many times with various patterns of scenarios or parameters. Such repeating execution brings about big redundancy because the change from a prior scenario to a later scenario is very minor in most cases, for example, blocking only one of roads or changing the speed limit of several roads. In this paper, we propose a new redundancy reduction technique, called exact-differential simulation, which enables to simulate only changing scenarios in later execution while keeping exactly same results as in the case of whole simulation. The paper consists of two main efforts: (i) a key idea and algorithm of the exact-differential simulation, (ii) a method to build large-scale traffic simulation on the top of the exact-differential simulation. In experiments of Tokyo traffic simulation, the exact-differential simulation shows 7.26 times as much elapsed time improvement in average and 2.26 times improvement even in the worst case as the whole simulation
Cooper Pair Formation in U(1) Gauge Theory of High Temperature Superconductivity
We study the two-dimensional spin-charge separated Ginzburg-Landau theory
containing U(1) gauge interactions as a semi-phenomenological model describing
fluctuating condensates in high temperature superconductivity. Transforming the
original GL action, we abstract the effective action of Cooper pair.
Especially, we clarify how Cooper pair correlation evolves in the normal state
from the point of view of spin-charge separation. Furthermore, we point out how
Cooper pair couples to gauge field in a gauge-invariant way, stressing the
insensitivity of Cooper pair to infrared gauge field fluctuation.Comment: 4 pages, 5 figures included, submitted to J. Phys. Soc. Jp
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