107 research outputs found
Superconductivity of a Metallic Stripe Embedded in an Antiferromagnet
We study a simple model for the metallic stripes found in
: two chain Hubbard ladder embedded in a static
antiferromagnetic environments. We consider two cases: a ``topological
stripe'', for which the phase of the Neel order parameter shifts by
across the ladder, and a ``non-topological stripe'', for which there is no
phase shift across the ladder. We perform one-loop renormalization group
calculations to determine the low energy properties. We compare the results
with those of the isolated ladder and show that for small doping
superconductivity is enhanced in the topological stripe, and suppressed in the
non-topological one. In the topological stripe, the superconducting order
parameter is a mixture of a spin singlet component with zero momentum and a
spin triplet component with momentum . We argue that this mixture is
generic, and is due to the presence of a new term in the quantum
Ginzburg-Landau action. Some consequences of this mixing are discussed.Comment: 6 pages, 3 eps figure
Comparative legal analysis of health systems in the Russian Federation and Switzerland
This article is devoted to a comparative legal analysis of healthcare systems in Russia and in Switzerland. The fundamental differences are identified. The legal nature of the healthcare system, the implementation of state control in the field of healthcare in the Russian Federation and in Switzerland, as well as promising directions for overcoming them are reveale
Electronic Properties of Armchair Carbon Nanotubes : Bosonization Approach
The phase Hamiltonian of armchair carbon nanotubes at half-filling and away
from it is derived from the microscopic lattice model by taking the long range
Coulomb interaction into account. We investigate the low energy properties of
the system using the renormalization group method. At half-filling, the ground
state is a Mott insulator with spin gap, in which the bound states of electrons
at different atomic sublattices are formed. The difference from the recent
results [Phys. Rev. Lett. 79, 5082 (1997)] away half-filling is clarified.Comment: 4 pages, 1 figure, Revte
Latin American experience in constitutional and legal guarantees of freedom of the media
The objective of the research was to analyze the Latin American experience in constitutional guarantees regarding freedom of expression in the media. The document summarizes the results of a comparative legal study dedicated to the texts included in the constitutions of the Latin American states regarding the identification of norms that guarantee the freedom of the media in them. It has been established that most of the declared constitutions contain traditional guarantees of media freedom expressed in the legalization of this substantive freedom, its implementation without censorship and restrictions under the threat of responsibility for its abus
Low Energy Properties of the (n,n) Carbon Nanotubes
According to band theory, an ideal undoped (n,n) carbon nanotube is metallic.
We show that the electron-electron interaction causes it to become Mott
insulating with a spin gap. More interestingly, upon doping it develops
superconducting fluctuations.Comment: 5pages, 2eps figures, one reference added, final version, accepted to
PR
Universality of electron correlations in conducting carbon nanotubes
Effective low-energy Hamiltonian of interacting electrons in conducting
single-wall carbon nanotubes with arbitrary chirality is derived from the
microscopic lattice model. The parameters of the Hamiltonian show very weak
dependence on the chiral angle, which makes the low energy properties of
conducting chiral nanotubes universal. The strongest Mott-like electron
instability at half filling is investigated within the self-consistent harmonic
approximation. The energy gaps occur in all modes of elementary excitations and
estimate at eV.Comment: 4 pages, 2 figure
Predicting a Gapless Spin-1 Neutral Collective Mode branch for Graphite
Using the standard tight binding model of 2d graphite with short range
electron repulsion, we find a gapless spin-1, neutral collective mode branch
{\em below the particle-hole continuum} with energy vanishing linearly with
momenta at the and points in the BZ. This spin-1 mode has a wide
energy dispersion, 0 to and is not Landau damped. The `Dirac cone
spectrum' of electrons at the chemical potential of graphite generates our
collective mode; so we call this `spin-1 zero sound' of the `Dirac sea'.
Epithermal neutron scattering experiments, where graphite single crystals are
often used as analyzers (an opportunity for `self-analysis'!), and spin
polarized electron energy loss spectroscopy (SPEELS) can be used to confirm and
study our collective mode.Comment: 4 pages of LaTex file, 3 eps figure file
Signatures of Stripe Phases in Hole Doped
We study nickelate-centered and oxygen-centered stripe phases in doped
LaNiO materials. We use an inhomogeneous Hartree-Fock and
random-phase approximation approach including both electron-electron and
electron-lattice(e-l) coupling for a layer of LaNiO. We find that
whether the ground state after commensurate hole doping comprises Ni-centered
or O-centered charge-localized stripes depends sensitively on the e-l
interaction. With increasing e-l interaction strength, a continuous transition
from an O-centered stripe phase to a Ni-centered one is found. Various low- and
high-energy signatures of these two kinds of stripe phases are predicted, which
can clearly distinguish them. These signatures reflect the strongly correlated
spin-charge-lattice features in the vicinity of Ni-centered or O-centered
stripe domains. The importance of e-l interaction for recent experiments on
stripe phases is discussed.Comment: 11 pages, 12 figures, to appear in Phys.Rev.B(July 1,1998
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