844 research outputs found
In situ assessment of carbon nanotube diameter distribution with photoelectron spectroscopy
7 págs.; 6 figs.; 1 tab. ; PACS numberssd: 73.22.2f, 79.60.Jv, 61.46.1wIn situ UV-photoelectron spectroscopy (He I and He II) was performed on multiwalled carbon nanotubes (CNTs) with clearly differentiated diameter distributions. A significant dependence of valence- and conduction-band characteristics on the mean CNT diameter was observed, which was determined by high-resolution TEM and micro-Raman spectroscopy. The decrease of relative intensity of the π states at -3 eV in the He II experiments, indicative of increasing rehybridization between orbitals, was directly correlated with decreasing mean diameters. Furthermore, a progressive broadening of the unoccupied σ* band at 7.6 eV was found in the He I spectra. © 2005 The American Physical Society.J.W.S. is grateful to the Centre Interdisciplinaire de Microscopie
Electronique sCIMEd at the Ecole Polytechnique
Fédérale de Lausanne sEPFLd for access to TEM and technical
support. We also thank the National Centre of Competence
in Research for Nanosciences NCCRd and the Swiss
National Foundation for financial support.Peer Reviewe
Optical signatures of spin-orbit exciton in bandwidth-controlled Sr2IrO4 epitaxial films via high-concentration Ca and Ba doping
We have investigated the electronic and optical properties of (Sr1-xCax)2IrO4 (x=0-0.375) and (Sr1-yBay)2IrO4 (y=0-0.375) epitaxial thin films, in which the bandwidth is systematically tuned via chemical substitutions of Sr ions by Ca and Ba. Transport measurements indicate that the thin-film series exhibits insulating behavior, similar to the Jeff=1/2 spin-orbit Mott insulator Sr2IrO4. As the average A-site ionic radius increases from (Sr1-xCax)2IrO4 to (Sr1-yBay)2IrO4, optical conductivity spectra in the near-infrared region shift to lower energies, which cannot be explained by the simple picture of well-separated Jeff=1/2 and Jeff=3/2 bands. We suggest that the two-peak-like optical conductivity spectra of the layered iridates originates from the overlap between the optically forbidden spin-orbit exciton and the intersite optical transitions within the Jeff=1/2 band. Our experimental results are consistent with this interpretation as implemented by a multiorbital Hubbard model calculation: namely, incorporating a strong Fano-like coupling between the spin-orbit exciton and intersite d-d transitions within the Jeff=1/2 band. ? 2017 American Physical Society.113Ysciescopu
Room temperature Mott metal-insulator transition in V2O3compounds induced via strain-engineering
status: publishe
Self-generated magnetic flux in YBaCuO grain boundaries
Grain boundaries in YBaCuO superconducting films are
considered as Josephson junctions with a critical current density
alternating along the junction. A self-generated magnetic flux is treated both
analytically and numerically for an almost periodic distribution of .
We obtained a magnetic flux-pattern similar to the one which was recently
observed experimentally.Comment: 7 pages, 3 figure
Measurements of Proton, Helium and Muon Spectra at Small Atmospheric Depths with the BESS Spectrometer
The cosmic-ray proton, helium, and muon spectra at small atmospheric depths
of 4.5 -- 28 g/cm^2 were precisely measured during the slow descending period
of the BESS-2001 balloon flight. The variation of atmospheric secondary
particle fluxes as a function of atmospheric depth provides fundamental
information to study hadronic interactions of the primary cosmic rays with the
atmosphere.Comment: 21 pages, 11 figures, 4 table
Measurements of Atmospheric Antiprotons
We measured atmospheric antiproton spectra in the energy range 0.2 to 3.4
GeV, at sea level and at balloon altitude in the atmospheric depth range 4.5 to
26 g/cm^2. The observed energy spectra, including our previous measurements at
mountain altitude, were compared with estimated spectra calculated on various
assumptions regarding the energy distribution of antiprotons that interacted
with air nuclei.Comment: Accepted for publication in PL
Elastic modulus of multi-walled carbon nanotubes produced by catalytic chemical vapour deposition
Carbon nanotubes (CNTs) are ideal structures for use as reinforcement fibres in composite materials, due to their extraordinary mechanical properties, in particular high Young's modulus (E∼1TPa). Usually the high value of E is taken as granted for all types of carbon CNTs. Here we demonstrate that multi-walled carbon nanotubes (MWCNTs) produced by catalytic chemical vapour deposition (CCVD) have low moduli (E<100GPa) independently of their growth conditions. We attribute this to the presence of structural defects. Additional high-temperature annealing failed to improve the mechanical properties. This study urges a better control of the growth process in order to obtain high strength CCVD grown MWCNTs suitable for reinforcement in large-scale industrial application
Two dimensional V2O3 and its experimental feasibility as robust room-temperature magnetic Chern insulator
The possibility of dissipationless chiral edge states without the need of an external magnetic field in the quantum anomalous Hall effect (QAHE) offers a great potential in electronic/spintronic applications. The biggest hurdle for the realization of a room-temperature magnetic Chern insulator is to find a structurally stable material with a sufficiently large energy gap and Curie temperature that can be easily implemented in electronic devices. This work based on first-principle methods shows that a single atomic layer of V2O3 with honeycomb–kagome (HK) lattice is structurally stable with a spin-polarized Dirac cone which gives rise to a room-temperature QAHE by the existence of an atomic on-site spin–orbit coupling (SOC). Moreover, by a strain and substrate study, it was found that the quantum anomalous Hall system is robust against small deformations and can be supported by a graphene substrate.status: publishe
Measurements of 0.2 to 20 GeV/n cosmic-ray proton and helium spectra from 1997 through 2002 with the BESS spectrometer
We measured low energy cosmic-ray proton and helium spectra in the kinetic
energy range 0.215 - 21.5 GeV/n at different solar activities during a period
from 1997 to 2002. The observations were carried out with the BESS spectrometer
launched on a balloon at Lynn Lake, Canada. A calculation for the correction of
secondary particle backgrounds from the overlying atmosphere was improved by
using the measured spectra at small atmospheric depths ranging from 5 through
37 g/cm^2. The uncertainties including statistical and systematic errors of the
obtained spectra at the top of atmosphere are 5-7 % for protons and 6-9 % for
helium nuclei in the energy range 0.5 - 5 GeV/n.Comment: 27 pages, 7 Tables, 9 figures, Submitted to Astroparticle Physic
Spin-Peierls transition in NaV2O5 in high magnetic fields
We investigate the magnetic field dependence of the spin-Peierls transition
in NaVO in the field range 16T-30T. The transition temperature exhibits
a very weak variation with the field, suggesting a novel mechanism for the
formation of the spin-Peierls state. We argue that a charge ordering transition
accompanied by singlet formation is consistent with our observations.Comment: 4 pages, 3 figures, final version to appear in Phys. Rev. B (RC
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