118 research outputs found
Two-channel conduction in YbPtBi
We investigated transport, magnetotransport, and broadband optical properties
of the half-Heusler compound YbPtBi. Hall measurements evidence two types of
charge carriers: highly mobile electrons with a temperature-dependent
concentration and low-mobile holes; their concentration stays almost constant
within the investigated temperature range from 2.5 to 300 K. The optical
spectra (10 meV - 2.7 eV) can be naturally decomposed into contributions from
intra- and interband absorption processes, the former manifesting themselves as
two Drude bands with very different scattering rates, corresponding to the
charges with different mobilities. These results of the optical measurements
allow us to separate the contributions from electrons and holes to the total
conductivity and to implement a two-channel-conduction model for description of
the magnetotransport data. In this approach, the electron and hole mobilities
are found to be around 50000 and 10 cm/Vs at the lowest temperatures (2.5
K), respectively.Comment: 6 page
Electronic Scattering Effects in Europium-Based Iron Pnictides
In a comprehensive study, we investigate the electronic scattering effects in
EuFe(AsP) by using Fourier-transform infrared
spectroscopy. In spite of the fact that Eu local moments order around
\,K, the overall optical response is strikingly similar
to the one of the well-known Ba-122 pnictides. The main difference lies within
the suppression of the lower spin-density-wave gap feature. By analysing our
spectra with a multi-component model, we find that the high-energy feature
around 0.7\,eV -- often associated with Hund's rule coupling -- is highly
sensitive to the spin-density-wave ordering, this further confirms its direct
relationship to the dynamics of itinerant carriers. The same model is also used
to investigate the in-plane anisotropy of magnetically detwinned
EuFeAs in the antiferromagnetically ordered state, yielding a
higher Drude weight and lower scattering rate along the crystallographic
-axis. Finally, we analyse the development of the room temperature spectra
with isovalent phosphor substitution and highlight changes in the scattering
rate of hole-like carriers induced by a Lifshitz transition
Optical conductivity of the Weyl semimetal NbP
The optical properties of (001)-oriented NbP single crystals have been
studied in a wide spectral range from 6 meV to 3 eV from room temperature down
to 10 K. The itinerant carriers lead to a Drude-like contribution to the
optical response; we can further identify two pronounced phonon modes and
interband transitions starting already at rather low frequencies. By comparing
our experimental findings to the calculated interband optical conductivity, we
can assign the features observed in the measured conductivity to certain
interband transitions. In particular, we find that transitions between the
electronic bands spilt by spin-orbit coupling dominate the interband
conductivity of NbP below 100 meV. At low temperatures, the momentum-relaxing
scattering rate of the itinerant carriers in NbP is very small, leading to
macroscopic characteristic length scales of the momentum relaxation of
approximately 0.5 m.Comment: 7.5 page
Clinical prodromes of neurodegeneration in Anderson-Fabry disease
To estimate the prevalence of prodromal clinical features of neurodegeneration in patients with Anderson-Fabry disease (AFD) in comparison to age-matched controls
Atomic oxygen number densities in the mesosphere–lower thermosphere region measured by solid electrolyte sensors on WADIS-2
Absolute profiles of atomic oxygen number densities with high vertical
resolution have been determined in the mesosphere–lower thermosphere (MLT) region from in situ
measurements by several rocket-borne solid electrolyte sensors. The
amperometric sensors were operated in both controlled and uncontrolled modes
and with various orientations on the foredeck and aft deck of the payload.
Calibration was based on mass spectrometry in a molecular beam containing
atomic oxygen produced in a microwave discharge. The sensor signal is
proportional to the number flux onto the electrodes, and the mass flow rate in
the molecular beam was additionally measured to derive this quantity from the
spectrometer reading. Numerical simulations provided aerodynamic correction
factors to derive the atmospheric number density of atomic oxygen from the
sensor data. The flight results indicate a preferable orientation of the
electrode surface perpendicular to the rocket axis. While unstable during the
upleg, the density profiles measured by these sensors show an excellent
agreement with the atmospheric models and photometer results during the
downleg of the trajectory. The high spatial resolution of the measurements
allows for the identification of small-scale variations in the atomic oxygen
concentration.</p
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