276 research outputs found
Superconductivity and Charge Density Wave in a Quasi-One-Dimensional Spin Gap System
We consider a model of spin-gapped chains weakly coupled by Josephson and
Coulomb interactions. Combining such non-perturbative methods as bosonization
and Bethe ansatz to treat the intra-chain interactions with the Random Phase
Approximation for the inter-chain couplings and the first corrections to this,
we investigate the phase diagram of this model. The phase diagram shows both
charge density wave ordering and superconductivity. These phases are seperated
by a line of critical points which exhibits an approximate an SU(2) symmetry.
We consider the effects of a magnetic field on the system. We apply the theory
to the material Sr_2 Ca_12 Cu_24 O_41 and suggest further experiments.Comment: 14 pages, 7 figure; submitted to PRB; Revised with new version:
references added; section on the flux state remove
Strongly correlated fermions with nonlinear energy dispersion and spontaneous generation of anisotropic phases
Using the bosonization approach we study fermionic systems with a nonlinear
dispersion relation in dimension d>2. We explicitly show how the band curvature
gives rise to interaction terms in the bosonic version of the model. Although
these terms are perturbatively irrelevant in relation to the Landau Fermi
liquid fixed point, they become relevant perturbations when instabilities take
place. Using a coherent state path integral technique we built up the effective
action that governs the dynamics of the Fermi surface fluctuations. We consider
the combined effect of fermionic interactions and band curvature on possible
anisotropic phases triggered by negative Landau parameters. In particular we
study in some detail the phase diagram for the isotropic/nematic/hexatic
quantum phase transition.Comment: RevTeX4, 9 pages, 2 eps figures, Final version as appeared in
Phys.Rev.
Coulomb Blockade Regime of a Single-Wall Nanotube
A model of carbon nanotube at half filling is studied. The Coulomb
interaction is assumed to be unscreened. It is shown that this allows to
develop the adiabatic approximation which leads to considerable simplifications
in calculations of the excitation spectrum. We give a detailed analysis of the
spectrum and the phase diagram at half filling and discuss effects of small
doping. At small doping several phases develop strong superconducting
fluctuations corresponding to various types of pairing
Interacting Electrons on a Fluctuating String
We consider the problem of interacting electrons constrained to move on a
fluctuating one-dimensional string. An effective low-energy theory for the
electrons is derived by integrating out the string degrees of freedom to lowest
order in the inverse of the string tension and mass density, which are assumed
to be large. We obtain expressions for the tunneling density of states, the
spectral function and the optical conductivity of the system. Possible
connections with the phenomenology of the cuprate high temperature
superconductors are discussed.Comment: 14 pages, 1 figur
Anderson-Yuval approach to the multichannel Kondo problem
We analyze the structure of the perturbation expansion of the general
multichannel Kondo model with channel anisotropic exchange couplings and in the
presence of an external magnetic field, generalizing to this case the
Anderson-Yuval technique. For two channels, we are able to map the Kondo model
onto a generalized resonant level model. Limiting cases in which the equivalent
resonant level model is solvable are identified. The solution correctly
captures the properties of the two channel Kondo model, and also allows an
analytic description of the cross-over from the non Fermi liquid to the Fermi
liquid behavior caused by the channel anisotropy.Comment: 23 pages, ReVTeX, 4 figures av. on reques
Theory of the Quantum Hall Smectic Phase II: Microscopic Theory
We present a microscopic derivation of the hydrodynamic theory of the Quantum
Hall smectic or stripe phase of a two-dimensional electron gas in a large
magnetic field. The effective action of the low energy is derived here from a
microscopic picture by integrating out high energy excitations with a scale of
the order the cyclotron energy.The remaining low-energy theory can be expressed
in terms of two canonically conjugate sets of degrees of freedom: the
displacement field, that describes the fluctuations of the shapes of the
stripes, and the local charge fluctuations on each stripe.Comment: 20 pages, RevTex, 3 figures, second part of cond-mat/0105448 New and
improved Introduction. Final version as it will appear in Physical Review
Kondo effect in crossed Luttinger liquids
We study the Kondo effect in two crossed Luttinger liquids, using Boundary
Conformal Field Theory. We predict two types of critical behaviors: either a
two-channel Kondo fixed point with a nonuniversal Wilson ratio, or a new theory
with an anomalous response identical to that found by Furusaki and Nagaosa (for
the Kondo effect in a single Luttinger liquid). Moreover, we discuss the
relevance of perturbations like channel anisotropy, and we make links with the
Kondo effect in a two-band Hubbard system modeled by a channel-dependent
Luttinger Hamiltonian. The suppression of backscattering off the impurity
produces a model similar to the four-channel Kondo theory.Comment: 7 pages, RevteX, to be published in Physical Review
Dynamical spin correlations in Heisenberg ladder under magnetic field and correlation functions in SO(5) ladder
The zero-temperature dynamical spin-spin correlation functions are calculated
for the spin-1/2 two-leg Heisenberg ladder in a magnetic field above the lower
critical field Hc1. The dynamical structure factors are calculated which
exhibit both massless and massive excitations. These modes appear in different
sectors characterized by the parity in the rung direction and by the momentum
in the direction of the chains. The structure factors have power-law
singularities at the lower edges of their support. The results are also
applicable to spin-1 Heisenberg chain. The implications are briefly discussed
for various correlation functions and the pi-resonance in the SO(5) symmetric
ladder model.Comment: 15 pages, 6 figures, added references; final version to appear in
Phys. Rev.
Moisture susceptibility of high and low compaction dry process crumb rubber modified asphalt mixtures
The field performance of dry process crumb rubber-modified (CRM) asphalt mixtures has been reported to be inconsistent with stripping and premature cracking on the surfacing. One of the concerns is that, because achieving field compaction of CRM material is difficult due to the inherent resilient nature of the rubber particle, nonuniform field compaction may lead to a deficient bond between rubber and bitumen. To assess the influence of compaction, a series of CRM and control mixtures was produced and compacted at two levels: 4% (low, optimum laboratory compaction) and 8% (high, field experience) air void content. The long-term durability, in regard to moisture susceptibility of the mixtures, was assessed by conducting repeated moisture conditioning cycles. Mechanical properties (stiffness, fatigue, and resistance to permanent deformation) were determined in the Nottingham Asphalt Tester. Results indicated that compared with conventional mixtures, the CRM mixtures, regardless of compaction effort, are more susceptible to moisture with the degree of susceptibility primarily depending on the amount of rubber in the mixture, rather than the difference in compaction. This behavior is different from that of conventional mixtures in which, as expected, poorly compacted mixtures were found to be more susceptible to moisture than were well-compacted mixtures
High prevalence of radiographic erosions in early, untreated PsA: results from the SpARRO cohort
Aims
To investigate the prevalence and distribution
of bone erosions in an early psoriatic arthritis (PsA)
population using conventional radiography (CR) and to
explore the agreement between CR and ultrasound (US)
detected bone erosions.
Methods
Newly diagnosed, treatment naïve PsA patients
fulfilling the ClASsification for Psoriatic Arthritis (CASPAR)
classification criteria of ≤5 years symptom duration
were recruited as part of the Leeds Spondyloarthropathy
Register for Research and Observation and underwent CR
and US examination of hands and feet.
Results
Overall, 4655 hand and feet joints were assessed
in 122 patients. CR erosions were detected in 24.6%
(n=30) with lowest prevalence seen below 8 months of
symptoms (17.5% vs 24.3%>24 months). The number of
erosions was higher on CR (1.55% (63/4,655); US 1.04%
(34/3,270)), with 5th metatarsophalangeal (MTP) joint
being the most affected site in both CR (5.21% (11/211))
and US (7.14% (15/210)). Erosions in CR were more evenly
distributed compared with US where three-quarters of the
total number of bone erosions were detected in wrists,
second metacarpophalangeal (MCP) and fifth MTP joints.
Most joints had almost perfect prevalence-adjusted bias-adjusted kappa values ranging from 0.91 to 1.
Conclusions
Erosions were seen in a quarter of patients
with newly diagnosed, untreated PsA with a declining trend
around the 8-month symptom duration cut-off. High levels
of agreement between CR and US were seen with CR
detecting more erosions. A focused US assessment of the
wrist, second MCP and fifth MTP joints may be useful to
detect bone erosions in early PsA
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