404 research outputs found
An experimental setup for high resolution 10.5 eV laser-based angle-resolved photoelectron spectroscopy using a time-of-flight electron analyzer
We present an experimental setup for laser-based angle-resolved
time-of-flight (LARTOF) photoemission. Using a picosecond pulsed laser, photons
of energy 10.5 eV are generated through higher harmonic generation in xenon.
The high repetition rate of the light source, variable between 0.2-8 MHz,
enables high photoelectron count rates and short acquisition times. By using a
Time-of-Flight (ToF) analyzer with angle-resolving capabilities electrons
emitted from the sample within a circular cone of up to \pm15 degrees can be
collected. Hence, simultaneous acquisition of photoemission data for a complete
area of the Brillouin zone is possible. The current photon energy enables bulk
sensitive measurements, high angular resolution and the resulting covered
momentum space is large enough to enclose the entire Brillouin zone in cuprate
high-Tc superconductors. Fermi edge measurements on polycrystalline Au shows an
energy resolution better than 5 meV. Data from a test measurement of the
Au(111) surface state is presented along with measurements of the Fermi surface
of the high-Tc superconductor Bi2212.Comment: 9 pages, 7 figure
A spin- and angle-resolving photoelectron spectrometer
A new type of hemispherical electron energy analyzer that permits angle and
spin resolved photoelectron spectroscopy has been developed. The analyzer
permits standard angle resolved spectra to be recorded with a two-dimensional
detector in parallel with spin detection using a mini-Mott polarimeter. General
design considerations as well as technical solutions are discussed and test
results from the Au(111) surface state are presented
Direct observation of decoupled Dirac states at the interface between topological and normal insulators
Several proposed applications and exotic effects in topological insulators
rely on the presence of helical Dirac states at the interface between a
topological and a normal insulator. In the present work, we have used
low-energy angle-resolved photoelectron spectroscopy to uncover and
characterize the interface states of BiSe thin films and
BiTe/BiSe heterostuctures grown on Si(111). The results
establish that Dirac fermions are indeed present at the
topological-normal-insulator boundary and absent at the
topological-topological-insulator interface. Moreover, it is demonstrated that
band bending present within the topological-insulator films leads to a
substantial separation of the interface and surface states in energy. These
results pave the way for further studies and the realization of
interface-related phenomena in topological-insulator thin-film
heterostructures.Comment: 9 pages, 5 figure
The J_{eff}=1/2 insulator Sr3Ir2O7 studied by means of angle-resolved photoemission spectroscopy
The low-energy electronic structure of the J_{eff}=1/2 spin-orbit insulator
Sr3Ir2O7 has been studied by means of angle-resolved photoemission
spectroscopy. A comparison of the results for bilayer Sr3Ir2O7 with available
literature data for the related single-layer compound Sr2IrO4 reveals
qualitative similarities and similar J_{eff}=1/2 bandwidths for the two
materials, but also pronounced differences in the distribution of the spectral
weight. In particuar, photoemission from the J_{eff}=1/2 states appears to be
suppressed. Yet, it is found that the Sr3Ir2O7 data are in overall better
agreement with band-structure calculations than the data for Sr2IrO4.Comment: 5 pages, 3 figure
Magnetic Order in the 2D Heavy-Fermion System CePt2In7 studied by muSR
The low-temperature microscopic magnetic properties of the quasi-2D
heavyfermion compound, CePt2In7 are investigated by using a positive muon-spin
rotation and relaxation (?muSR) technique. Clear evidence for the formation of
a commensurate antiferromagnetic order below TN=5.40 K is presented. The
magnetic order parameter is shown to fit well to a modified BSC gap-energy
function in a strong-coupling scenario.Comment: Accepted in Journal of Physics: Conference Series (2014
Nodal Landau Fermi-Liquid Quasiparticles in Overdoped LaSrCuO
Nodal angle resolved photoemission spectra taken on overdoped
LaSrCuO are presented and analyzed. It is proven that the
low-energy excitations are true Landau Fermi-liquid quasiparticles. We show
that momentum and energy distribution curves can be analyzed self-consistently
without quantitative knowledge of the bare band dispersion. Finally, by
imposing Kramers-Kronig consistency on the self-energy , insight into
the quasiparticle residue is gained. We conclude by comparing our results to
quasiparticle properties extracted from thermodynamic, magneto-resistance, and
high-field quantum oscillation experiments on overdoped
TlBaCuO.Comment: Accepted for publication in Phys. Rev.
Laboratory diagnosis of Lyme neuroborreliosis: a comparison of three CSF anti-Borrelia antibody assays
The diagnosis of Lyme neuroborreliosis (LNB) requires the detection of intrathecal synthesis of Borrelia-specific antibodies, but in very early disease, the sensitivity may be low. We compared the performance of the second-generation IDEIA Lyme Neuroborreliosis test (Oxoid), based on purified native flagellum antigen, with two newly developed tests based on several recombinant antigens for the diagnosis of LNB. Patients investigated for LNB during 2003 through 2007 were included (n = 175); 52 with definite LNB, four with possible LNB and 119 non-LNB patients. Serum and cerebrospinal fluid (CSF) were analysed with the IDEIA Lyme Neuroborreliosis (Oxoid), VIDAS Lyme IgG (bioMérieux) and recomBead Borrelia IgM and IgG (Mikrogen) assays. Intrathecal antibody indices (AIs) were calculated according to the manufacturers’ protocols. The IDEIA test performed with an overall sensitivity (IgM and IgG AIs taken together) of 88 % and a specificity of 99 %. The VIDAS test showed a sensitivity of 86 % and a specificity of 97 %. An overall sensitivity of 100 % and a specificity of 97 % were achieved by the recomBead test. We conclude that the three assays performed equally well regarding specificity, but our data suggest an improved diagnostic sensitivity with the recomBead Borrelia test
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