11,231 research outputs found
Superconducting and normal-state properties of the noncentrosymmetric superconductor Re6Zr
We systematically investigate the normal and superconducting properties of
non-centrosymmetric ReZr using magnetization, heat capacity, and
electrical resistivity measurements. Resistivity measurements indicate
ReZr has poor metallic behavior and is dominated by disorder. ReZr
undergoes a superconducting transition at K. Magnetization measurements give a lower critical
field, mT. The
Werthamer-Helfand-Hohenberg model is used to approximate the upper critical
field T which is close to
the Pauli limiting field of 12.35 T and which could indicate singlet-triplet
mixing. However, low-temperature specific-heat data suggest that ReZr is
an isotropic, fully gapped s-wave superconductor with enhanced electron-phonon
coupling. Unusual flux pinning resulting in a peak effect is observed in the
magnetization data, indicating an unconventional vortex state.Comment: 11 pages, 7 figures, 2 table
Probing the superconducting ground state of the noncentrosymmetric superconductors CaTSi3 (T = Ir, Pt) using muon-spin relaxation and rotation
The superconducting properties of CaTSi3 (where T = Pt and Ir) have been
investigated using muon spectroscopy. Our muon-spin relaxation results suggest
that in both these superconductors time-reversal symmetry is preserved, while
muon-spin rotation data show that the temperature dependence of the superfluid
density is consistent with an isotropic s-wave gap. The magnetic penetration
depths and upper critical fields determined from our transverse-field muon-spin
rotation spectra are found to be 448(6) and 170(6) nm, and 3800(500) and
1700(300) G, for CaPtSi3 and CaIrSi3 respectively. The superconducting
coherence lengths of the two materials have also been determined and are 29(2)
nm for CaPtSi3 and 44(4) nm for CaIrSi3.Comment: 6 pages, 7 figure
Comparative study of the centrosymmetric and non-centrosymmetric superconducting phases of Re3W using muon-spin spectroscopy and heat capacity measurements
We compare the low-temperature electronic properties of the centrosymmetric
(CS) and non-centrosymmetric (NCS) phases of Re3W using muon-spin spectroscopy
and heat capacity measurements. The zero-field muSR results indicate that
time-reversal symmetry is preserved for both structures of Re3W.
Transverse-field muon spin rotation has been used to study the temperature
dependence of the penetration depth lambda(T) in the mixed state. For both
phases of Re3W, lambda(T) can be explained using a single-gap s-wave BCS model.
The magnetic penetration depth at zero temperature, lambda(0), is 164(7) and
418(6) nm for the centrosymmetric and the non-centrosymmetric phases of Re3W
respectively. Low-temperature specific heat data also provide evidence for an
s-wave gap-symmetry for the two phases of Re3W. Both the muSR and heat capacity
data show that the CS material has a higher Tc and a larger superconducting gap
Delta(0) at 0 K than the NCS compound. The ratio Delta(0)/kBTc indicates that
both phases of Re3W should be considered as strong-coupling superconductors.Comment: 7 pages, to appear in Physical Review
Contemporary outcome measures in acute stroke research: choice of primary outcome measure
BACKGROUND AND PURPOSE:
The diversity of available outcome measures for acute stroke trials is challenging and implies that the scales may be imperfect. To assist researchers planning trials and to aid interpretation, this article reviews and makes recommendations on the available choices of scales. The aim is to identify an approach that will be universally accepted and that should be included in most acute trials, without seeking to restrict options for special circumstances.
METHODS:
The article considers outcome measures that have been widely used or are currently advised. It examines desirable properties for outcome measures such as validity, relevance, responsiveness, statistical properties, availability of training, cultural and language issues, resistance to comorbidity, as well as potential weaknesses. Tracking and agreement among outcomes are covered.
RESULTS:
Typical ranges of scores for the common scales are described, along with their statistical properties, which in turn influence optimal analytic techniques. The timing of recovery on scores and usual practice in trial design are considered.
CONCLUSIONS:
The preferred outcome measure for acute trials is the modified Rankin Scale, assessed at 3 months after stroke onset or later. The interview should be conducted by a certified rater and should involve both the patient and any relevant caregiver. Incremental benefits at any level of the modified Rankin Scale may be acceptable. The modified Rankin Scale is imperfect but should be retained in its present form for comparability with existing treatment comparisons. No second measure should be required, but correlations with supporting scales may be used to confirm consistency in direction of effects on other measures
Magnetic phase diagram of the antiferromagnetic pyrochlore Gd2Ti2O7
Gd2Ti2O7 is a highly frustrated antiferromagnet on a pyrochlore lattice,
where apart from the Heisenberg exchange the spins also interact via
dipole-dipole forces. We report on low-temperature specific heat measurements
performed on single crystals of Gd2Ti2O7 for three different directions of an
applied magnetic field. The measurements reveal the strongly anisotropic
behaviour of Gd2Ti2O7 in a magnetic field despite the apparent absence of a
significant single-ion anisotropy for Gd3+. The H-T phase diagrams are
constructed for H//111], H//[110] and H//[112]. The results indicate that
further theoretical work beyond a simple mean-field model is required.Comment: 4 figure
Studies of the superconducting properties of Sn1-xInxTe (x=0.38 to 0.45) using muon-spin spectroscopy
The superconducting properties of Sn1-xInxTe (x = 0.38 to 0.45) have been
studied using magnetization and muon-spin rotation or relaxation (muSR)
measurements. These measurements show that the superconducting critical
temperature Tc of Sn1-xInxTe increases with increasing x, reaching a maximum at
around 4.8 K for x = 0.45. Zero-field muSR results indicate that time-reversal
symmetry is preserved in this material. Transverse-field muon-spin rotation has
been used to study the temperature dependence of the magnetic penetration depth
lambda(T) in the mixed state. For all the compositions studied, lambda(T) can
be well described using a single-gap s-wave BCS model. The magnetic penetration
depth at zero temperature lambda(0) ranges from 500 to 580 nm. Both the
superconducting gap Delta(0) at 0 K and the gap ratio Delta(0)/kBTc indicate
that Sn1-xInxTe (x = 0.38 to 0.45) should be considered as a superconductor
with intermediate to strong coupling.Comment: 7 pages, 6 figures, 3 table
Static magnetic moments revealed by muon spin relaxation and thermodynamic measurements in quantum spin ice YbTiO
We present muon spin relaxation (SR) and specific-heat versus
temperature measurements on polycrystalline and single-crystal samples
of the pyrochlore magnet YbTiO. exhibits a sharp peak at a
of 0.21 and 0.26~K for the single-crystal and polycrystalline
samples respectively. For both samples, the magnetic entropy released between
50~mK and 30~K amounts to per Yb. At temperatures below
we observe a steep drop in the asymmetry of the zero-field SR time spectra
at short time scales, as well as a decoupling of the muon spins from the
internal field in longitudinal magnetic fields of ~T for both the
polycrystalline and single-crystal samples. These muon data are indicative of
static magnetic moments. Our results are consistent with the onset of
long-range magnetic order in both forms of YbTiO.Comment: 6 pages, 4 figures, accepted to PR
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