616 research outputs found
Spin Gap Fixed Points in the Double Chain Problem
Applying the bosonization procedure to weakly coupled Hubbard chains we
discuss the fixed points of the renormalization group flow where all spin
excitations are gapful and a singlet pairing becomes the dominant instability.Comment: 15 pages, TeX, C Version 3.
Scaling Properties of the Two-Chain Model
Scaling properties of a self-dual field-theoretical model, describing two
weakl$spinless Luttinger chains, are studied. A crossover to a sine-Gordon
massive phase, with strongly developed two-particleinterchain correlations, is
described. It is argued that, in a wide range of the in-chain interaction,
renormalization of the interchain hopping amplitude is determined by the
Luttinger liquid effects.Comment: 14 pages Latex, accepted Physics Letters
Role of Umklapp Processes in Conductivity of Doped Two-Leg Ladders
Recent conductivity measurements performed on the hole-doped two-leg ladder
material reveal an approximately linear
power law regime in the c-axis DC resistivity as a function of temperature for
. In this work, we employ a bosonic model to argue that umklapp processes
are responsible for this feature and for the high spectral weight in the
optical conductivity which occurs beyond the finite frequency Drude-like peak.
Including quenched disorder in our model allows us to reproduce experimental
conductivity and resistivity curves over a wide range of energies. We also
point out the differences between the effect of umklapp processes in a single
chain and in the two-leg ladder.Comment: 10 pages, 2 figure
Impurity effects in unconventional density waves in the unitary limit
We investigate the effect of strong, nonmagnetic impurities on
quasi-one-dimensional conventional and unconventional density waves (DW and
UDW). The conventional case remains unaffected similarly to s-wave
superconductors in the presence of weak, nonmagnetic impurities. The
thermodynamic properties of UDW were found to be identical to those of a d-wave
superconductor in the unitary limit. The real and imaginary part of the optical
conductivity is determined for electric fields applied in the perpendicular
directions. A new structure can be present corresponding to excitations from
the bound state at the Fermi energy to the gap maximum in addition to the usual
peak at 2\Delta. In the dc limit, universal electric conductivity is found.Comment: 9 pages, 5 figure
Superconductivity from correlated hopping
We consider a chain described by a next-nearest-neighbor hopping combined
with a nearest-neighbor spin flip. In two dimensions this three-body term
arises from a mapping of the three-band Hubbard model for CuO planes to a
generalized model and for large O-O hopping favors resonance-valence-bond
superconductivity of predominantly -wave symmetry. Solving the ground state
and low-energy excitations by analytical and numerical methods we find that the
chain is a Luther-Emery liquid with correlation exponent , where is the particle density.Comment: 10 pages, RevTeX 3.0 + 2 PostScript figs. Accepted for publication in
Phys.Rev.
Critical properties of the double-frequency sine-Gordon model with applications
We study the properties of the double-frequency sine--Gordon model in the
vicinity of the Ising quantum phase transition displayed by this model. Using a
mapping onto a generalised lattice quantum Ashkin-Teller model, we obtain
critical and nearly-off-critical correlation functions of various operators. We
discuss applications of the double-sine-Gordon model to one-dimensional
physical systems, like spin chains in a staggered external field and
interacting electrons in a staggered potential.Comment: 51 pages, Latex fil
Integer Programming: Optimization and Evaluation Are Equivalent
Link to conference publication published by Springer: http://dx.doi.org/10.1007/978-3-642-03367-4We show that if one can find the optimal value of an integer linear programming problem in polynomial time, then one can find an optimal solution in polynomial time. We also present a proper generalization to (general) integer programs and to local search problems of the well-known result that optimization and augmentation are equivalent for 0/1-integer programs. Among other things, our results imply that PLS-complete problems cannot have “near-exact” neighborhoods, unless PLS = P.United States. Office of Naval Research (ONR grant N00014-01208-1-0029
Spin chirality induced by the Dzyaloshinskii-Moriya interaction and the polarized neutron scattering
We discuss the influence of the Dzyaloshinskii-Moriya (DM) interaction in the
Heizenberg spin chain model for the observables in the polarized neutron
scattering experiments. We show that different choices of the parameters of DM
interaction may leave the spectrum of the problem unchanged, while the
observable spin-spin correlation functions may differ qualitatively.
Particularly, for the uniform DM interaction one has the incommensurate
fluctuations and polarization-dependent neutron scattering in the paramagnetic
phase. We sketch the possible generalization of our treatment to higher
dimensions.Comment: 4 pages, REVTEX, no figures, references added, to appear in PR
Imperfect nesting and transport properties in unconventional density waves
We consider the effect of imperfect nesting in quasi-one dimensional
unconventional density waves.
The phase diagram is very close to those in a conventional DW. The linear and
non-linear aspects of the electric conductivity are discussed. At T=0 the
frequency dependent electric conductivity develops a small dip at low
frequencies.
The threshold electric field depends strongly on the imperfect nesting
parameter, allowing us to describe the measured threshold electric field in the
low temperature phase of the quasi-two dimensional organic conductor,
alpha-(BEDT-TTF)_2KHg(SCN)_4 very well.Comment: 9 pages, 9 figure
Disorder Effects in Two-Dimensional d-wave Superconductors
Influence of weak nonmagnetic impurities on the single-particle density of
states of two-dimensional electron systems with a conical
spectrum is studied. We use a nonperturbative approach, based on replica trick
with subsequent mapping of the effective action onto a one-dimensional model of
interacting fermions, the latter being treated by Abelian and non-Abelian
bosonization methods. It is shown that, in a d-wave superconductor, the density
of states, averaged over randomness, follows a nontrivial power-law behavior
near the Fermi energy: . The exponent
is calculated for several types of disorder. We demonstrate that the
property is a direct consequence of a {\it continuous} symmetry
of the effective fermionic model, whose breakdown is forbidden in two
dimensions. As a counter example, we consider another model with a conical
spectrum - a two-dimensional orbital antiferromagnet, where static disorder
leads to a finite due to breakdown of a {\it discrete}
(particle-hole) symmetry.Comment: 24 pages, 3 figures upon request, RevTe
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