517 research outputs found
Quasi-Langmuir-Blodgett Thin Film Deposition of Carbon Nanotubes
The handling and manipulation of carbon nanotubes continues to be a challenge
to those interested in the application potential of these promising materials.
To this end, we have developed a method to deposit pure nanotube films over
large flat areas on substrates of arbitrary composition. The method bears some
resemblance to the Langmuir-Blodgett deposition method used to lay down thin
organic layers. We show that this redeposition technique causes no major
changes in the films' microstructure and that they retain the electronic
properties of as-deposited film laid down on an alumina membrane.Comment: 3 pages, 3 figures, submitted Journal of Applied Physic
Observation of correlations up to the micrometer scale in sliding charge-density waves
High-resolution coherent x-ray diffraction experiment has been performed on
the charge density wave (CDW) system KMoO. The satellite
reflection associated with the CDW has been measured with respect to external
dc currents. In the sliding regime, the satellite reflection displays
secondary satellites along the chain axis which corresponds to correlations up
to the micrometer scale. This super long range order is 1500 times larger than
the CDW period itself. This new type of electronic correlation seems inherent
to the collective dynamics of electrons in charge density wave systems. Several
scenarios are discussed.Comment: 4 pages, 3 figures Typos added, references remove
Landau quantization effects in the charge-density-wave system (Per)(mnt) (where Au and Pt)
A finite transfer integral orthogonal to the conducting chains of a
highly one-dimensional metal gives rise to empty and filled bands that simulate
an indirect-gap semiconductor upon formation of a commensurate
charge-density-wave (CDW). In contrast to semiconductors such as Ge and Si with
bandgaps eV, the CDW system possesses an indirect gap with a greatly
reduced energy scale, enabling moderate laboratory magnetic fields to have a
major effect. The consequent variation of the thermodynamic gap with magnetic
field due to Zeeman splitting and Landau quantization enables the electronic
bandstructure parameters (transfer integrals, Fermi velocity) to be determined
accurately. These parameters reveal the orbital quantization limit to be
reached at T in (Per)(mnt) salts, making them highly
unlikely candidates for a recently-proposed cascade of field-induced
charge-density wave states
Character of electron reflection at a normal metal-Peierls semiconductor boundary
The reflection of electrons incident from a normal metal on the boundary of
the metal with a quasi-one-dimensional conductor containing a charge-density
wave (CDW) is investigated theoretically. It is shown that the reflection is
not of an Andreev character, as it was suggested earlier, but rather of a Bragg
character. This is due to the fact that the CDW is actually an electronic
crystal, and its wave vector is a reciprocal lattice vector of the electronic
crystal. The ratio of the intensities of the standard and Bragg reflection
depends on the phase of the CDW.Comment: 9 pages, no figures, revte
Wick's Theorem and a New Perturbation Theory Around the Atomic Limit of Strongly Correlated Electron Systems
A new type of perturbation expansion in the mixing of localized orbitals
with a conduction-electron band in the Anderson model is
presented. It is built on Feynman diagrams obeying standard rules. The local
correlations of the unperturbed system (the atomic limit) are included exactly,
no auxiliary particles are introduced. As a test, an infinite-order ladder-type
resummation is analytically treated in the Kondo regime, recovering the correct
energy scale. An extension to the Anderson-lattice model is obtained via an
effective-site approximation through a cumulant expansion in on the
lattice. Relation to treatments in infinite spatial dimensions are indicated.Comment: selfextracting postscript file containing entire paper (10 pages)
including 3 figures, in case of trouble contact author for LaTeX-source or
hard copies (prep0994
Theoretical Study of Friction: A Case of One-Dimensional Clean Surfaces
A new method has been proposed to evaluate the frictional force in the
stationary state. This method is applied to the 1-dimensional model of clean
surfaces. The kinetic frictional force is seen to depend on velocity in
general, but the dependence becomes weaker as the maximum static frictional
force increases and in the limiting case the kinetic friction gets only weakly
dependent on velocity as described by one of the laws of friction. It is also
shown that there is a phase transition between state with vanishing maximum
static frictional force and that with finite one. The role of randomness at the
interface and the relation to the impurity pinning of the sliding
Charge-Density-Wave are discussed. to appear in Phys.Rev.B. abstract only. Full
text is available upon request. E-mail: [email protected]: 2 pages, Plain TEX, OUCMT-94-
Evidence of Spatially Inhomogeous Pairing on the Insulating Side of a Disorder-Tuned Superconductor-Insulator Transition
Measurements of transport properties of amorphous insulating indium oxide
thin films have been interpreted as evidence of the presence of superconducting
islands on the insulating side of a disorder-tuned superconductor-insulator
transition. Although the films are not granular, the behavior is similar to
that observed in granular films. The results support theoretical models in
which the destruction of superconductivity by disorder produces spatially
inhomogenous pairing with a spectral gap.Comment: Revised title and content/argument. Totals: 4 pages, 3 figure
Recommended from our members
SERS analysis of Ag nanostructures produced by ion-beam deposition
This study deals with the development of a novel technique for formation of advanced Ag nanostructures (NSs) to be applied to high-resolution analyses based on surface enhanced Raman scattering (SERS). It has direct bearing on human health and food quality, e.g., monitoring small amount or traces of pollutants or undesirable additives. Three types of nanostructured Ag samples were produced using ion-beam deposition at glancing angle (GLAD) on quartz. All fabricated structures were covered with BI-58 pesticide (dimethoate) or Rhodamine 6G (R6G) for testing their potential for use as substrates for (SERS)
Electrodynamics of a Coulomb Glass in n-type Silicon
Optical measurements of the real and imaginary frequency dependent
conductivity of uncompensated n-type silicon are reported. The experiments are
done in the quantum limit, , across a broad doping range
on the insulating side of the Metal-Insulator transition (MIT). The observed
low energy linear frequency dependence shows characteristics consistent with
theories of a Coulomb glass, but discrepancies exist in the relative magnitudes
of the real and imaginary components. At higher energies we observe a crossover
to a quadratic frequency dependence that is sharper than expected over the
entire dopant range. The concentration dependence gives evidence that the
Coulomb interaction energy is the relevant energy scale that determines this
crossover.Comment: 5 pages, 4 figures; accepted for publication in Phys. Rev. Let
- …