321 research outputs found
Interplay between phase defects and spin polarization in the specific heat of the spin density wave compound (TMTTF)_2Br in a magnetic field
Equilibrium heat relaxation experiments provide evidence that the ground
state of the commensurate spin density wave (SDW) compound (TMTTF)Br after
the application of a sufficient magnetic field is different from the
conventional ground state. The experiments are interpreted on the basis of the
local model of strong pinning as the deconfinement of soliton-antisoliton pairs
triggered by the Zeeman coupling to spin degrees of freedom, resulting in a
magnetic field induced density wave glass for the spin carrying phase
configuration.Comment: 4 pages, 5 figure
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
Anomalous Spin and Charge Dynamics of the 2D t-J Model at low doping
We present an exact diagonalization study of the dynamical spin and density
correlation function of the 2D t-J model for hole doping < 25%. Both
correlation functions show a remarkably regular, but completely different
scaling behaviour with both hole concentration and parameter values: the
density correlation function is consistent with that of bosons corresponding to
the doped holes and condensed into the lowest state of the noninteracting band
of width 8t, the spin correlation function is consistent with Fermions in a
band of width J. We show that the spin bag picture gives a natural explanation
for this unusual behaviour.Comment: Revtex-file, 4 PRB pages + 5 figures attached as uu-encoded ps-files
Hardcopies of figures (or the entire manuscript) can also be obtained by
e-mailing to: [email protected]
Spinless fermions ladders at half filling
We study a half filled ladder of spinless fermions. We show that contrarily
to a single chain, the ladder becomes a Mott insulator for arbitrarily small
repulsive interactions. We obtain the full phase diagram and physical
quantities such as the charge gap. We show that there is only a single
insulating phase for repulsive interactions, regardless of the stength of the
interchain hopping and single chain Mott gap. There is thus no
confinement-deconfinement transition in this system but a simple crossover. We
show that upon doping the system becomes a Luttinger liquid with a universal
parameter different from the one of the single chain ().Comment: 9 pages, 6 figures, uses revtex4 beta4 and natbib(included);
submitted to PR
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
Does the attractive Hubbard model support larger persistent currents than the repulsive one ?
We consider a one-dimensional Hubbard model in the presence of disorder. We
compute the charge stiffness for a mesoscopic ring, as a function of the size
, which is a measure of the permanent currents. We find that for finite
disorder the permanent currents of the system with repulsive interactions are
larger than those of the system with attractive interactions. This counter
intuitive result is due to the fact that local density fluctuations are reduced
in the presence of repulsive interactions.Comment: 14 pages; Revtex 3.0; 3 postscript figures uuencoded with uufile
Charge Excitations in Doped Mott Insulator in One Dimension
The doped Mott insulator in one dimension has been studied based on the phase
Hamiltonian with the Umklapp scattering process, in which the charge degree of
freedom is described by the quantum sine-Gordon model. The well-known
equivalence between the quantum sine-Gordon model and the massive Thirring
model for the spinless fermion makes it clear that the Mott-Hubbard gap
originates from the Umklapp scattering process as was indicated by Emery and
Giamarchi. Compressibility, density-density correlation function, frequency
dependence of optical conductivity and Drude weight have been calculated in the
presence of the impurity scattering treated in the self-consistent Born
approximation. It is seen that there exists a crossover behavior in the
spectral weight of charge excitations: the acoustic mode is dominant in small
wave number region while the optical excitations across the Mott-Hubbard gap
lie in large wave number region and that this crossover wave number is reduced
as the Mott transition is approached.Comment: We revised our previous manuscript. 17 pages and 11 figures, to be
published in Journal of the Physical Society of Japan Vol.65 No.1
Quantized Conductance of One-Dimensional Doped Mott Insulator
The possible modification of quantized conductance of one-dimensional doped
Mott insulator, where the Umklapp scattering plays an important role, is
studied based on the method by Maslov-Stone and Ponomarenko. At T=0 and away
from half-filling, the conductance is quantized as and there is no
renormalization by Umklapp scattering process. At finite temperatures, however,
the quantization is affected depending on the gate voltage and temperature.Comment: 10 pages, 4 figures, uses jpsj.st
Effects of a weak disorder on two coupled Hubbard chains
We consider the effect of weak nonmagnetic disorder on two chains of
interacting fermions (with and without spins) coupled by interchain hopping.
For the spinless case, interchain hopping increases localization for repulsive
interactions but {\it stabilizes} the s-wave superconducting phase for
attractive interactions. For the case with spin, the d-wave phase arising from
purely repulsive interactions in the clean system is destroyed by an
infinitesimal disorder while for attractive interactions, the s-wave
superconductivity is more resistant to disorder than in the one-chain case.Comment: 12 pages, ReVTeX ,paper submitted to PR
On the Spin Gap Phase of Strongly-Correlated Electrons
We discuss the possible existence of a spin-gap phase in the low-doping
regime of strongly-correlated two-dimensional electrons within the gauge field
description of the t-J model. The spin-gap phase was recently shown by Ubbens
and Lee to be destroyed by gauge field quantum fluctuations for a single-layer
2D system in the absence of disorder and for a full gap. We show that the same
conclusion applies both in the dirty limit and for the case of a gapless spinon
condensate.Comment: 7 pages, uuencoded Postscript, including 1 figur
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