113 research outputs found
Spin Gap and Superconductivity in Weakly Coupled Ladders: Interladder One-particle vs. Two-particle Crossover
Effects of the interladder one-particle hopping, , on the
low-energy asymptotics of a weakly coupled Hubbard ladder system have been
studied, based on the perturbative renormalization-group approach. We found
that for finite intraladder Hubbard repulsion, , there exists a crossover
value of the interladder one-particle hopping, . For
, the spin gap metal (SGM) phase of the isolated
ladder transits at a finite transition temperature, , to the d-wave
superconducting (SCd) phase via a two-particle crossover. In the temperature
region, , interladder coherent Josephson tunneling of the Cooper pairs
occurs, while the interladder coherent one-particle process is strongly
suppressed. For , around a crossover temperature,
, the system crosses over to the two-dimensional (2D) phase via a
one-particle crossover. In the temperature region, , the
interladdercoherent band motion occurs.Comment: 4 pages, 5 eps figures, uses jpsj.st
Interchain coherence of coupled Luttinger liquids at all orders in perturbation theory
We analyze the problem of Luttinger liquids coupled via a single-particle
hopping \tp and introduce a systematic diagrammatic expansion in powers of
\tp. An analysis of the scaling of the diagrams at each order allows us to
determine the power-law behavior versus \tp of the interchain hopping and of
the Fermi surface warp. In particular, for strong interactions, we find that
the exponents are dominated by higher-order diagrams producing an enhanced
coherence and a failure of linear-response theory. Our results are valid at any
finite order in \tp for the self-energy.Comment: 4 pages, 3 ps figures. Accepted for publication in Phys. Rev. Let
Hall Effect in a Quasi-One-Dimensional System
We consider the Hall effect in a system of weakly coupled one-dimensional
chains with Luttinger interaction within each chain. We construct a
perturbation theory in the inter-chain hopping term and find that there is a
power law dependence of the Hall conductivity on the magnetic field with an
exponent depending on the interaction constant. We show that this perturbation
theory becomes valid if the magnetic field is sufficiently large.Comment: 20 page
One particle interchain hopping in coupled Hubbard chains
Interchain hopping in systems of coupled chains of correlated electrons is
investigated by exact diagonalizations and Quantum-Monte-Carlo methods. For two
weakly coupled Hubbard chains at commensurate densities (e.g. n=1/3) the
splitting at the Fermi level between bonding and antibonding bands is strongly
reduced (but not suppressed) by repulsive interactions extending to a few
lattice spacings. The magnitude of this reduction is directly connected to the
exponent of the 1D Luttinger liquid. However, we show that the
incoherent part of the single particle spectral function is much less affected
by the interchain coupling. This suggests that incoherent interchain hopping
could occur for intermediate values.Comment: 4 pages, LaTeX 3.0, 7 PostScript figures in uuencoded for
Dimensional crossover and metal-insulator transition in quasi-two-dimensional disordered conductors
We study the metal-insulator transition (MIT) in weakly coupled disordered
planes on the basis of a Non-Linear Sigma Model (NLM). Using two
different methods, a renormalization group (RG) approach and an auxiliary field
method, we calculate the crossover length between a 2D regime at small length
scales and a 3D regime at larger length scales. The 3D regime is described by
an anisotropic 3D NLM with renormalized coupling constants. We obtain
the critical value of the single particle interplane hopping which separates
the metallic and insulating phases. We also show that a strong parallel
magnetic field favors the localized phase and derive the phase diagram.Comment: 16 pages (RevTex), 4 poscript figure
Hubbard chains network on corner-sharing tetrahedra: origin of the heavy fermion state in LiV_2O_4
We investigate the Hubbard chains network model defined on corner-sharing
tetrahedra (the pyrochlore lattice) which is a possible microscopic model for
the heavy fermion state of LiV_2O_4. Based upon this model, we can explain
transport, magnetic, and thermodynamic properties of LiV_2O_4. We calculate the
spin susceptibility, and the specific heat coefficient, exploiting the Bethe
ansatz exact solution of the 1D Hubbard model and bosonization method. The
results are quite consistent with experimental observations. We obtain the
large specific heat coefficient .Comment: 5 pages, 2 figures, a postscript file of Figure 1 is not included, to
appear in Physical Review
Impurity-induced stabilization of Luttinger liquid in quasi-one-dimensional conductors
It is shown theoretically that the Luttinger liquid phase in
quasi-one-dimensional conductors can exist in the presence of impurities in a
form of a collection of bounded Luttinger liquids. The conclusion is based upon
the observation by Kane and Fisher that a local impurity potential in Luttinger
liquid acts, at low energies, as an infinite barrier. This leads to a discrete
spectrum of collective charge and spin density fluctuations, so that interchain
hopping can be considered as a small parameter at temperatures below the
minimum excitation energy of the collective modes. The results are compared
with recent experimental observation of a Luttinger-liquid-like behavior in
thin NbSe and TaS wires.Comment: 11 pages, revtex, final version published in JETP Lett
Strong-Coupling Expansion for the Hubbard Model
A strong-coupling expansion for models of correlated electrons in any
dimension is presented. The method is applied to the Hubbard model in
dimensions and compared with numerical results in . Third order expansion
of the Green function suffices to exhibit both the Mott metal-insulator
transition and a low-temperature regime where antiferromagnetic correlations
are strong. It is predicted that some of the weak photoemission signals
observed in one-dimensional systems such as should become stronger as
temperature increases away from the spin-charge separated state.Comment: 4 pages, RevTex, 3 epsf figures include
Optical conductivity of one-dimensional Mott insulators
We calculate the optical conductivity of one-dimensional Mott insulators at
low energies using a field theory description. The square root singularity at
the optical gap, characteristic of band insulators, is generally absent and
appears only at the Luther-Emery point. We also show that only few particle
processes contribute significantly to the optical conductivity over a wide
range of frequencies and that the bare perturbative regime is recovered only at
very large energies. We discuss possible applications of our results to quasi
one-dimensional organic conductors.Comment: 4 pages, 3 figures results adde
Spin-Density-Wave Phase Transitions in Quasi-One-Dimensional Dimerized Quarter-Filled Organic Conductors
We have studied spin density wave (SDW) phase transitions in dimerized
quarter-filled Hubbard chains weakly coupled via interchain one-particle
hopping, . It is shown that there exists a critical value of ,
, between the incoherent metal regime () and the
Fermi liquid regime () in the metallic phase above the SDW
transition temperature. By using the 2-loop perturbative renormalization-group
approach together with the random-phase-approximation, we propose a SDW phase
diagram covering both of the regimes. The SDW phase transition from the
incoherent metal phase for is caused by growth of the
intrachain electron-electron umklapp scattering toward low temperatures, which
is regarded as preformation of the Mott gap. We discuss relevance of the
present result to the SDW phase transitions in the quasi-one-dimensional
dimerized quarter-filled organic conductors, (TMTTF)X and (TMTSF)X.Comment: 19 pages, 13 eps figures, uses jpsj.sty, corrected typo in the text
and figures, no changes to the paper, to appear in J. Phys. Soc. Jpn. 68,
No.8 (1999
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