749 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
Correlated Quantum Transport of Density Wave Electrons
Recently observed Aharonov-Bohm quantum interference of period h/2e in charge
density wave rings strongly suggest that correlated density wave electron
transport is a cooperative quantum phenomenon. The picture discussed here
posits that quantum solitons nucleate and transport current above a Coulomb
blockade threshold field. We propose a field-dependent tunneling matrix element
and use the Schrodinger equation, viewed as an emergent classical equation as
in Feynman's treatment of Josephson tunneling, to compute the evolving
macrostate amplitudes, finding excellent quantitative agreement with voltage
oscillations and current-voltage characteristics in NbSe3. A proposed phase
diagram shows the conditions favoring soliton nucleation versus classical
depinning. (Published in Phys. Rev. Lett. 108, 036404 (2012).)Comment: 9 pages, 4 figures, (5 pages & 3 figures for main article), includes
Supplemental Material with 1 figure. Published version: Physical Review
Letters, vol. 108, p. 036404 (2012
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Glancing angle deposition of sculptured thin metal films at room temperature
Metallic thin films consisting of separated nanostructures are fabricated by evaporative glancing angle deposition at room temperature. The columnar microstructure of the Ti and Cr columns is investigated by high resolution transmission electron microscopy and selective area electron diffraction. The morphology of the sculptured metallic films is studied by scanning electron microscopy. It is found that tilted Ti and Cr columns grow with a single crystalline morphology, while upright Cr columns are polycrystalline. Further, the influence of continuous substrate rotation on the shaping of Al, Ti, Cr and Mo nanostructures is studied with view to surface diffusion and the shadowing effect. It is observed that sculptured metallic thin films deposited without substrate rotation grow faster compared to those grown with continuous substrate rotation. A theoretical model is provided to describe this effect
Peierls instability, periodic Bose-Einstein condensates and density waves in quasi-one-dimensional boson-fermion mixtures of atomic gases
We study the quasi-one-dimensional (Q1D) spin-polarized bose-fermi mixture of
atomic gases at zero temperature. Bosonic excitation spectra are calculated in
random phase approximation on the ground state with the uniform BEC, and the
Peierls instabilities are shown to appear in bosonic collective excitation
modes with wave-number by the coupling between the Bogoliubov-phonon
mode of bosonic atoms and the fermion particle-hole excitations. The
ground-state properties are calculated in the variational method, and,
corresponding to the Peierls instability, the state with a periodic BEC and
fermionic density waves with the period are shown to have a lower
energy than the uniform one. We also briefly discuss the Q1D system confined in
a harmonic oscillator (HO) potential and derive the Peierls instability
condition for it.Comment: 9 pages, 3figure
Strictly One-Dimensional Electron System in Au Chains on Ge(001) Revealed By Photoelectron K-Space Mapping
Atomic nanowires formed by Au on Ge(001) are scrutinized for the band
topology of the conduction electron system by k-resolved photoemission. Two
metallic electron pockets are observed. Their Fermi surface sheets form
straight lines without undulations perpendicular to the chains within
experimental uncertainty. The electrons hence emerge as strictly confined to
one dimension. Moreover, the system is stable against a Peierls distortion down
to 10 K, lending itself for studies of the spectral function. Indications for
unusually low spectral weight at the chemical potential are discussed.Comment: 4 pages, 4 figures - revised version with added Fig. 2e) and
additional reference
Hmga2 is dispensable for pancreatic cancer development, metastasis, and therapy resistance.
Expression of the chromatin-associated protein HMGA2 correlates with progression, metastasis and therapy resistance in pancreatic ductal adenocarcinoma (PDAC). Hmga2 has also been identified as a marker of a transient subpopulation of PDAC cells that has increased metastatic ability. Here, we characterize the requirement for Hmga2 during growth, dissemination, and metastasis of PDAC in vivo using conditional inactivation of Hmga2 in well-established autochthonous mouse models of PDAC. Overall survival, primary tumour burden, presence of disseminated tumour cells in the peritoneal cavity or circulating tumour cells in the blood, and presence and number of metastases were not significantly different between mice with Hmga2-wildtype or Hmga2-deficient tumours. Treatment of mice with Hmga2-wildtype and Hmga2-deficient tumours with gemcitabine did not uncover a significant impact of Hmga2-deficiency on gemcitabine sensitivity. Hmga1 and Hmga2 overlap in their expression in both human and murine PDAC, however knockdown of Hmga1 in Hmga2-deficient cancer cells also did not decrease metastatic ability. Thus, Hmga2 remains a prognostic marker which identifies a metastatic cancer cell state in primary PDAC, however Hmga2 has limited if any direct functional impact on PDAC progression and therapy resistance
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
Disentanglement of the electronic and lattice parts of the order parameter in a 1D Charge Density Wave system probed by femtosecond spectroscopy
We report on the high resolution studies of the temperature (T) dependence of
the q=0 phonon spectrum in the quasi one-dimensional charge density wave (CDW)
compound K0.3MoO3 utilizing time-resolved optical spectroscopy. Numerous modes
that appear below Tc show pronounced T-dependences of their amplitudes,
frequencies and dampings. Utilizing the time-dependent Ginzburg-Landau theory
we show that these modes result from linear coupling of the electronic part of
the order parameter to the 2kF phonons, while the (electronic) CDW amplitude
mode is overdamped.Comment: 4 pages, 3 figures + supplementary material, accepted for publication
in Phys. Rev. Let
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-
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