277 research outputs found
Comparison of wind measurements between a Mini-SODAR PA0, a METEK-SODAR and a 99 m tower
Doppler-SODAR measurements are commonly used to derive the vertical wind profile. One main advantage of the Mini-SODAR (from the company Remtech) is its small size and weight and therefore it is easy to handle and set up in short time. Two long-term measurements were operated in September and October 2009. A statistical comparison was made between the Mini-SODAR, the tower and the DWD-SODAR (from the company METEK) for the two measurement periods. It is presented here that the Mini-SODAR overestimates the tower measurements and also the
measurements of the DWD-SODAR. It is also shown, that the Mini-SODAR is able to determine the mean flow conditions in the lower boundary layer (up to 200 m)
Orbital selectivity causing anisotropy and particle-hole asymmetry in the charge density wave gap of -TaS
We report an in-depth Angle Resolved Photoemission Spectroscopy (ARPES) study
on -TaS, a canonical incommensurate Charge Density Wave (CDW) system.
This study demonstrates that just as in related incommensurate CDW systems,
-TaSe and -NbSe, the energy gap () of
-TaS is localized along the K-centered Fermi surface barrels and is
particle-hole asymmetric. The persistence of even at
temperatures higher than the CDW transition temperature
in -TaS, reflects the similar pseudogap (PG) behavior observed
previously in -TaSe and -NbSe. However, in sharp contrast to
-NbSe, where is non-zero only in the vicinity
of a few "hot spots" on the inner K-centered Fermi surface barrels,
in -TaS is non-zero along the entirety of both
K-centered Fermi surface barrels. Based on a tight-binding model, we attribute
this dichotomy in the momentum dependence and the Fermi surface specificity of
between otherwise similar CDW compounds to the
different orbital orientations of their electronic states that are involved in
CDW pairing. Our results suggest that the orbital selectivity plays a critical
role in the description of incommensurate CDW materials.Comment: 6 pages, 4 figure
Ferromagnetism and Superconductivity in the multi-orbital Hubbard Model: Hund's Rule Coupling versus Crystal-Field Splitting
The multi-orbital Hubbard model in one dimension is studied using the
numerical diagonalization method. Due to the effect of the crystal-field
splitting , the fully polarized ferromagnetism which is observed in the
strong coupling regime becomes unstable against the partially polarized
ferromagnetism when the Hund's rule coupling is smaller than a certain
critical value of order of . In the vicinity of the partially polarized
ferromagnetism, the orbital fluctuation develops due to the competition between
the Hund's rule coupling and the crystal-field splitting. The superconducting
phase with the Luttinger liquid parameter is observed for the
singlet ground state in this region.Comment: 4 pages,5 figures,submitted to J.Phys.Soc.Jp
Investigation of the spin-glass regime between the antiferromagnetic and superconducting phases in FeSeTe
Using bulk magnetization along with elastic and inelastic neutron scattering
techniques, we have investigated the phase diagram of
FeSeTe and the nature of magnetic correlations in three
nonsuperconducting samples of FeSeTe,
FeSeTe and FeSeTe. A cusp
and hysteresis in the temperature dependence of the magnetization for the
and 0.3 samples indicates spin-glass (SG) ordering below K. Neutron scattering measurements indicate that the spin-glass behavior is
associated with short-range spin density wave (SDW) ordering characterized by a
static component and a low-energy dynamic component with a characteristic
incommensurate wave vector of and an anisotropy
gap of 2.5 meV. Our high -resolution data also show that the
systems undergo a glassy structural distortion that coincides with the
short-range SDW order
Evidence for charge localization in the ferromagnetic phase of La_(1-x)Ca_(x)MnO_3 from High real-space-resolution x-ray diffraction
High real-space-resolution atomic pair distribution functions of
La_(1-x)Ca_(x)MnO_3 (x=0.12, 0.25 and 0.33) have been measured using
high-energy x-ray powder diffraction to study the size and shape of the MnO_6
octahedron as a function of temperature and doping. In the paramagnetic
insulating phase we find evidence for three distinct bond-lengths (~ 1.88, 1.95
and 2.15A) which we ascribe to Mn^{4+}-O, Mn^{3+}-O short and Mn^{3+}-O long
bonds respectively. In the ferromagnetic metallic (FM) phase, for x=0.33 and
T=20K, we find a single Mn-O bond-length; however, as the metal-insulator
transition is approached either by increasing T or decreasing x, intensity
progressively appears around r=2.15 and in the region 1.8 - 1.9A suggesting the
appearance of Mn^{3+}-O long bonds and short Mn^{4+}-O bonds. This is strong
evidence that charge localized and delocalized phases coexist close to the
metal-insulator transition in the FM phase.Comment: 8 pages, 8 postscript figures, submitted to Phys. Rev.
Magnetic-field-induced collapse of charge-ordered nanoclusters and the Colossal Magnetoresistance effect in Nd(0.3)Sr(0.3)MnO(3)
We report synchrotron x-ray scattering studies of charge/orbitally ordered
(COO) nanoclusters in NdSrMnO. We find that the COO
nanoclusters are strongly suppressed in an applied magnetic field, and that
their decreasing concentration follows the field-induced decrease of the sample
electrical resistivity. The COO nanoclusters, however, do not completely
disappear in the conducting state, suggesting that this state is inhomogeneous
and contains an admixture of an insulating phase. Similar results were also
obtained for the zero-field insulator-metal transition that occurs as
temperature is reduced. These observations suggest that these correlated
lattice distortions play a key role in the Colossal Magnetoresistance effect in
this prototypical manganite.Comment: 5 pages, 3 embedded eps figures; to appear in PRB Rapid
Commumication
Polaron Absorption in a Perovskite Manganite La0.7Ca0.3MnO3
Temperature dependent optical conductivity spectra of a La0.7Ca0.3MnO3 (LCMO)
sample were measured. In the metallic regime at very low temperatures, they
clearly showed two types of absorption features, i.e., a sharp Drude peak and a
broad mid-infrared absorption band, which could be explained as coherent and
incoherent bands of a large lattice polaron. This elementary excitation in LCMO
was found to be in a strong coupling regime and to have interactions with the
spin degree of freedom.Comment: 4 pages and separate 4 figure
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