1,377 research outputs found
Solar vane actuator Patent
Design and characteristics of device for sensing solar radiation and providing spacecraft attitude control to maintain direction with respect to incident radiatio
Attitude control for spacecraft Patent
Attitude control system for spacecraft based on conversion of incident solar radiation on movable control surfaces into mechanical torque
Magnetotransport in the CeIrIn system: The influence of antiferromagnetic fluctuations
We present an overview of magnetotransport measurements on the heavy-fermion
superconductor CeIrIn. Sensitive measurements of the Hall effect and
magnetoresistance (MR) are used to elucidate the low temperature phase diagram
of this system. The normal-state magnetotransport is highly anomalous, and
experimental signatures of a pseudogap-like precursor state to
superconductivity as well as evidence for two distinct scattering times
governing the Hall effect and the MR are observed. Our observations point out
the influence of antiferromagnetic fluctuations on the magnetotransport in this
class of materials. The implications of these findings, both in the context of
unconventional superconductivity in heavy-fermion systems as well as in
relation to the high temperature superconducting cuprates are discussed
Magnetic structure of Cd-doped CeCoIn5
The heavy fermion superconductor CeCoIn5 is believed to be close to a
magnetic instability, but no static magnetic order has been found. Cadmium
doping on the In-site shifts the balance between superconductivity and
antiferromagnetism to the latter with an extended concentration range where
both types of order coexist at low temperatures. We investigated the magnetic
structure of nominally 10% Cd-doped CeCoIn5, being antiferromagnetically
ordered below T_N=3 K and superconducting below T_c=1.3 K, by elastic neutron
scattering. Magnetic intensity was observed only at the ordering wave vector
Q_AF = (1/2,1/2,1/2) commensurate with the crystal lattice. Upon entering the
superconducting state the magnetic intensity seems to change only little. The
commensurate magnetic ordering in CeCo(In1-xCdx)5 is in contrast to the
incommensurate antiferromagnetic ordering observed in the closely related
compound CeRhIn5. Our results give new insights in the interplay between
superconductivity and magnetism in the family of CeTIn5 (T=Co, Rh, and Ir)
based compounds.Comment: 4 pages, 4 figure
Two Superconducting Phases in CeRh_1-xIr_xIn_5
Pressure studies of CeRh_1-xIr_xIn_5 indicate two superconducting phases as a
function of x, one with T_c >= 2 K for x < 0.9 and the other with T_c < 1.2 K
for x > 0.9. The higher T_c phase, phase-1, emerges in proximity to an
antiferromagnetic quantum-critical point; whereas, Cooper pairing in the lower
T_c phase-2 is inferred to arise from fluctuations of a yet to be found
magnetic state. The T-x-P phase diagram of CeRh_1-xIr_xIn_5, though
qualitatively similar, is distinctly different from that of
CeCu_2(Si_1-xGe_x)_2.Comment: 5 pages, 3 figure
Possible re-entrant superconductivity in EuFe2As2 under pressure
We studied the temperature-pressure phase diagram of EuFe2As2 by measurements
of the electrical resistivity. The antiferromagnetic spin-density-wave
transition at T_0 associated with the FeAs-layers is continuously suppressed
with increasing pressure, while the antiferromagnetic ordering temperature of
the Eu 2+ moments seems to be nearly pressure independent up to 2.6 GPa. Above
2 GPa a sharp drop of the resistivity, \rho(T), indicates the onset of
superconductivity at T_c \approx 29.5 K. Surprisingly, on further reducing the
temperature \rho(T) is increasing again and exhibiting a maximum caused by the
ordering of the Eu 2+ moments, a behavior which is reminiscent of re-entrant
superconductivity as it is observed in the ternary Chevrel phases or in the
rare-earth nickel borocarbides
Interplay between Freezing and Superconductivity in the Optimally Doped LaEu0.20Sr0.15CuO4 under Hydrostatic Pressure
We study the electronic properties of a LaEu0.20Sr0.15CuO4 single crystal
under hydrostatic pressure up to 2.9 GPa. Both the freezing of the Cu 3d
moments and the structural transition from the orthorhombic (LTO) to the
tetragonal (LTT) phase are observed via the relaxation of the nuclear
magnetization of La nuclei. Resistivity and magnetic susceptibility
measurements have been carried out under pressure on the same sample. The
combination of all data reveals the connection between glassy dynamics, charge
localization and the disappearance of superconductivity in the LTT phase.Comment: 5 pages, 4 figures, submitte
On the search for the chiral anomaly in Weyl semimetals: The negative longitudinal magnetoresistance
Recently, the existence of massless chiral (Weyl) fermions has been
postulated in a class of semi-metals with a non-trivial energy dispersion.These
materials are now commonly dubbed Weyl semi-metals (WSM).One predicted property
of Weyl fermions is the chiral or Adler-Bell-Jackiw anomaly, a chirality
imbalance in the presence of parallel magnetic and electric fields. In WSM, it
is expected to induce a negative longitudinal magnetoresistance (NMR), the
chiral magnetic effect.Here, we present experimental evidence that the
observation of the chiral magnetic effect can be hindered by an effect called
"current jetting". This effect also leads to a strong apparent NMR, but it is
characterized by a highly non-uniform current distribution inside the sample.
It appears in materials possessing a large field-induced anisotropy of the
resistivity tensor, such as almost compensated high-mobility semimetals due to
the orbital effect.In case of a non-homogeneous current injection, the
potential distribution is strongly distorted in the sample.As a consequence, an
experimentally measured potential difference is not proportional to the
intrinsic resistance.Our results on the MR of the WSM candidate materials NbP,
NbAs, TaAs, TaP exhibit distinct signatures of an inhomogeneous current
distribution, such as a field-induced "zero resistance' and a strong dependence
of the `measured resistance" on the position, shape, and type of the voltage
and current contacts on the sample. A misalignment between the current and the
magnetic-field directions can even induce a "negative resistance".
Finite-element simulations of the potential distribution inside the sample,
using typical resistance anisotropies, are in good agreement with the
experimental findings. Our study demonstrates that great care must be taken
before interpreting measurements of a NMR as evidence for the chiral anomaly in
putative Weyl semimetals.Comment: 13 pages, 6 figure
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