60 research outputs found
The barocaloric effect: A Spin-off of the Discovery of High-Temperature Superconductivity
Some key results obtained in joint research projects with Alex M\"uller are
summarized, concentrating on the invention of the barocaloric effect and its
application for cooling as well as on important findings in the field of
high-temperature superconductivity resulting from neutron scattering
experiments.Comment: 26 pages, 9 figure
Superfluid Density and Angular Dependence of the Energy Gap inOptimally Doped (BiPb)2(SrLa)2CuO6+ δ
We present a muon-spin rotation study of the optimally doped cuprate superconductor (BiPb)2(SrLa)2 CuO6+δ . The measured magnetic field dependence of the in-plane magnetic penetration λ ab suggests superconductivity with a dominant d-wave order parameter. The comparison of the temperature dependence of λ ab with calculations, assuming the angular gap symmetry as obtained from photoemission measurements, is consistent with a partial suppression of the quasi-particle weight towards the anti-nodal region of the Fermi surface. This suggests that the superconducting and the pseudogap state are dominated by different parts of the Fermi surfac
Universal observation of multiple order parameters in cuprate superconductors
The temperature dependence of the London penetration depth \lambda was
measured for an untwined single crystal of YBa_2Cu_3O_{7-\delta} along the
three principal crystallographic directions (a, b, and c). Both in-plane
components (\lambda_a and \lambda_b) show an inflection point in their
temperature dependence which is absent in the component along the c-direction
(\lambda_c). The data provide convincing evidence that the in-plane
superconducting order parameter is a mixture of s+d-wave symmetry whereas it is
exclusively s-wave along the c-direction. In conjunction with previous results
it is concluded that coupled s+d-order parameters are universal and intrinsic
to cuprate superconductors.Comment: 5 pages, 3 figure
Direct observation of local Mn-Mn distances in the paramagnetic compound CsMnxMg1-xBr3
We introduce a novel method for local structure determination with a spatial
resolution of the order of 0.01 Angstroem. It can be applied to materials
containing clusters of exchange-coupled magnetic atoms. We use neutron
spectroscopy to probe the energies of the cluster excitations which are
determined by the interatomic coupling strength J. Since for most materials J
is related to the interatomic distance R through a linear relation
dJ/dR={\alpha} (for dR/R<<1), we can directly derive the local distance R from
the observed excitation energies. This is exemplified for the mixed
one-dimensional paramagnetic compound CsMnxMg1 xBr3 (x=0.05, 0.10) containing
manganese dimers oriented along the hexagonal c-axis. Surprisingly, the
resulting Mn-Mn distances R do not vary continuously with increasing internal
pressure, but lock in at some discrete values.Comment: 16 pages, 2 tables, 3 figure
Multidrug-resistant tuberculosis in prison inmates, Azerbaijan.
In a tuberculosis (TB) program in the Central Penitentiary Hospital of Azerbaijan, we analyzed 65 isolates of Mycobacterium tuberculosis by IS6110-based restriction fragment-length polymorphism (RFLP) and spoligotyping. From 11 clusters associated with 33 patients, 31 isolates had an IS6110-based banding pattern characteristic of the Beijing genotype of M. tuberculosis. In addition, 15 M. tuberculosis isolates with similar RFLP patterns constituted a single group by spoligotyping, matching the Beijing genotype. Multidrug resistance, always involving isoniazid and rifampin, was seen in 34 (52.3%) of 65 isolates, with 28 belonging to the Beijing genotype
New structural and magnetic aspects of the nanotube system Na2V3O7
We present new experimental results of low temperature x-ray synchrotron
diffraction, neutron scattering and very low temperature (mK-range) bulk
measurements on the nanotube system {\tube}. The crystal structure determined
from our data is similar to the previously proposed model (P. Millet {\it et
al.} J. Solid State Chem. , 676 (1999)), but also deviates from it in
significant details. The structure comprises nanotubes along the c-axis formed
by stacking units of two V-rings buckled in the -plane. The space group is
P and the composition is nonstoichiometric, Na(2-x)V3O7, x=0.17. The
thermal evolution of the lattice parameters reveals anisotropic lattice
compression on cooling. Neutron scattering experiments monitor a very weak
magnetic signal at energies from -20 to 9 meV. New magnetic susceptibility,
specific heat measurements and decay of remanent magnetization in the 30 mK -
300 mK range reveal that the previously observed transition at ~76 mK is
spin-glass like with no long-range order. Presented experimental observations
do not support models of isolated clusters, but are compatible with a model of
odd-legged S=1/2 spin tubes possibly segmented into fragments with different
lengths
Oxygen disorder in ice probed by X-ray Compton scattering
We use electron momentum density in ice as a tool to quantify order-disorder
transitions by comparing Compton profiles differences of ice VI, VII, VIII and
XII with respect to ice Ih. Quantitative agreement is found between theory and
experiment for ice VIII, which is the most ordered phase. Robust signatures of
the oxygen disorder are identified in the momentum density for the VIII-VII ice
phase transition. The unique aspect of this work is the determination of the
fraction n_e of electron directly involved in phase transitions as well as the
use of position space signatures for quantifying oxygen site disorder.Comment: 3 figures, 2 tables. Accepted for publication in Phys. Rev.
High pressure behavior of CsC8 graphite intercalation compound
International audienceThe high pressure phase diagram of CsC8 graphite intercalated compound has been investigated at ambient temperature up to 32 GPa. Combining X-ray and neutron diffraction, Raman and X- ray absorption spectroscopies, we report for the first time that CsC8, when pressurized, undergoes phase transitions around 2.0, 4.8 and 8 GPa. Possible candidate lattice structures and the transition mechanism involved are proposed. We show that the observed transitions involve the structural re- arrangement in the Cs sub-network while the distance between the graphitic layers is continuously reduced at least up to 8.9 GPa. Around 8 GPa, important modifications of signatures of the electronic structure measured by Raman and X-ray absorption spectroscopies evidence the onset of a new transition
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