4,946 research outputs found
Evidence for spin liquid ground state in SrDyO frustrated magnet probed by muSR
Muon spin relaxation (SR) measurements were carried out on
SrDyO, a frustrated magnet featuring short range magnetic correlations
at low temperatures. Zero-field muon spin depolarization measurements
demonstrate that fast magnetic fluctuations are present from K down to
20 mK. The coexistence of short range magnetic correlations and fluctuations at
mK indicates that SrDyO features a spin liquid ground state.
Large longitudinal fields affect weakly the muon spin depolarization, also
suggesting the presence of fast fluctuations. For a longitudinal field of
T, a non-relaxing asymmetry contribution appears below K,
indicating considerable slowing down of the magnetic fluctuations as
field-induced magnetically-ordered phases are approached.Comment: 6 pages, 4 figures, to be published as a proceeding of HFM2016 in
Journal of Physics: Conference Series (JPCS
Magnetic quantum critical point and superconductivity in UPt3 doped with Pd
Transverse-field muon spin relaxation measurements have been carried out on
the heavy-fermion superconductor UPt3 doped with small amounts of Pd. We find
that the critical Pd concentration for the emergence of the large-moment
antiferromagnetic phase is ~0.6 at.%Pd. At the same Pd content,
superconductivity is completely suppressed. The existence of a magnetic quantum
critical point in the phase diagram, which coincides with the critical point
for superconductivity, provides evidence for ferromagnetic spin-fluctuation
mediated odd-parity superconductivity, which competes with antiferromagnetic
order.Comment: 4 pages (includes 3 figures); postscript fil
Magnetic quantum critical point and superconductivity in UPt3 doped with Pd
Transverse-field muon spin relaxation measurements have been carried out on
the heavy-fermion superconductor UPt3 doped with small amounts of Pd. We find
that the critical Pd concentration for the emergence of the large-moment
antiferromagnetic phase is ~0.6 at.%Pd. At the same Pd content,
superconductivity is completely suppressed. The existence of a magnetic quantum
critical point in the phase diagram, which coincides with the critical point
for superconductivity, provides evidence for ferromagnetic spin-fluctuation
mediated odd-parity superconductivity, which competes with antiferromagnetic
order.Comment: 4 pages (includes 3 figures); postscript fil
THE DIFFERENTIAL GAS TURBINE USING ELECTRIC TRANSMISSION
ABSTRACT This paper describes studies of simple gas turbine engines integrated with electrical transmission components. Recent developments in high-speed lightweight electrical machines and compact power electronics have enabled alternators and motors to be produced which can be coupled directly to the shaft of a gas turbine without an intermediate gearbox. For applications which require a wide range of power outputs, a single-shaft gas turbine with a high speed alternator can be run at constant speed while varying the current drawn from the alternator. This combines the flexibility of operation of a separate power turbine with the simplicity of a single-shaft engine. With this arrangement, in traction use high torques are obtained at low speed, while near-constant engine efficiency is sustained to about 50% of the design power. In the differential engine, the mechanical linkage between the compressor and the turbine is replaced with an electrical linkage. The turbine drives an alternator, and part of the alternator power is taken by a highspeed motor to drive the compressor. The excess alternator power forms the output of the engine. The compressor and turbine are now able to run at different speeds, and their operating points can be separately optimised at different engine conditions. For such an engine, studies show that high efficiency can be maintained to low power levels
Magnetic field distribution and characteristic fields of the vortex lattice for a clean superconducting niobium sample in an external field applied along a three-fold axis
The field distribution in the vortex lattice of a pure niobium single crystal
with an external field applied along a three-fold axis has been investigated by
the transverse-field muon-spin-rotation (TF-SR) technique over a wide
range of temperatures and fields. The experimental data have been analyzed with
the Delrieu's solution for the form factor supplemented by phenomenological
formulas for the parameters. This has enabled us to experimentally establish
the temperatures and fields for the Delrieu's, Ginzburg-Landau's, and Klein's
regions of the vortex lattice. Using the numerical solution of the
quasiclassical Eilenberger's equation the experimental results have been
reasonably understood. They should apply to all clean BCS superconductors. The
analytical Delrieu's model supplemented by phenomenological formulas for its
parameters is found to be reliable for analyzing TF-SR experimental data
for a substantial part of the mixed phase. The Abrikosov's limit is contained
in it.Comment: 12 pages, 15 figure
Muon spin rotation and relaxation in the superconducting ferromagnet UCoGe
We report zero-field muon spin rotation and relaxation measurements on the
superconducting ferromagnet UCoGe. Weak itinerant ferromagnetic order is
detected by a spontaneous muon spin precession frequency below the Curie
temperature K. The precession frequency persists below the
bulk superconducting transition temperature K, where it measures
a local magnetic field T. The amplitude of the SR signal
provides unambiguous proof for ferromagnetism present in the whole sample
volume. We conclude ferromagnetism coexists with superconductivity on the
microscopic scale.Comment: 4 pages, 3 figures, accepted for publication in PR
Quantum spin chain as a potential realization of the Nersesyan-Tsvelik model
It is well established that long-range magnetic order is suppressed in
magnetic systems whose interactions are low-dimensional. The prototypical
example is the S-1/2 Heisenberg antiferromagnetic chain (S-1/2 HAFC) whose
ground state is quantum critical. In real S-1/2 HAFC compounds interchain
coupling induces long-range magnetic order although with a suppressed ordered
moment and reduced N\'eel temperature compared to the Curie-Weiss temperature.
Recently, it was suggested that order can also be suppressed if the interchain
interactions are frustrated, as for the Nersesyan-Tsvelik model. Here, we study
the new S-1/2 HAFC, (NO)[Cu(NO3)3]. This material shows extreme suppression of
order which furthermore is incommensurate revealing the presence of frustration
consistent with the Nersesyan-Tsvelik model
A new interferometric study of four exoplanet host stars : {\theta} Cygni, 14 Andromedae, {\upsilon} Andromedae and 42 Draconis
Studying exoplanet host stars is of the utmost importance to establish the
link between the presence of exoplanets around various types of stars and to
understand the respective evolution of stars and exoplanets.
Using the limb-darkened diameter (LDD) obtained from interferometric data, we
determine the fundamental parameters of four exoplanet host stars. We are
particularly interested in the F4 main-sequence star, {\theta} Cyg, for which
Kepler has recently revealed solar-like oscillations that are unexpected for
this type of star. Furthermore, recent photometric and spectroscopic
measurements with SOPHIE and ELODIE (OHP) show evidence of a quasi-periodic
radial velocity of \sim150 days. Models of this periodic change in radial
velocity predict either a complex planetary system orbiting the star, or a new
and unidentified stellar pulsation mode.
We performed interferometric observations of {\theta} Cyg, 14 Andromedae,
{\upsilon} Andromedae and 42 Draconis for two years with VEGA/CHARA (Mount
Wilson, California) in several three-telescope configurations. We measured
accurate limb darkened diameters and derived their radius, mass and temperature
using empirical laws.
We obtain new accurate fundamental parameters for stars 14 And, {\upsilon}
And and 42 Dra. We also obtained limb darkened diameters with a minimum
precision of \sim 1.3%, leading to minimum planet masses of Msini=5.33\pm 0.57,
0.62 \pm 0.09 and 3.79\pm0.29 MJup for 14 And b, {\upsilon} And b and 42 Dra b,
respectively. The interferometric measurements of {\theta} Cyg show a
significant diameter variability that remains unexplained up to now. We propose
that the presence of these discrepancies in the interferometric data is caused
by either an intrinsic variation of the star or an unknown close companion
orbiting around it.Comment: 10 pages + 2 pages appendix, 16 figures, accepted for publication in
A&
Magnetic order and spin dynamics in the proximity of a ferromagnetic quantum critical point: A {\mu}SR study of YbNi4P2
The local 4f-electronic spin dynamics and magnetic order in YbNi4P2 were
studied by means of muon-spin relaxation measurements. Zero-field muon-spin
relaxation proves static magnetic order with a strongly reduced ordered Yb3+
moment of (2.5-4.6) \times 10-2{\mu}B, below TC = 140 mK. Above TC, the
muon-spin polarization P(t,B) is dominated by quasihomogeneous spin
fluctuations and exhibits a time-field scaling relation P(t,B) =
P(t/B{\gamma}), indicating cooperative critical spin dynamics in the system. At
T = 190 mK, slightly above TC, {\gamma} = 0.81(5), suggesting time-scale
invariant power-law behavior for the dynamic electronic spin-spin
autocorrelation function.Comment: 5 pages, 4 figure
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