1,171 research outputs found
Bulk superconductivity in Bi4O4S3 revealed by specific heat measurement
Specific heat experiments on a well-characterized polycrystalline sample of
the BiS2 based superconductor Bi4O4S3 revealed that it shows a crear specific
heat anomaly at about Tc = 4.4 K, consistent with Tc from the resistivity and
dc susceptibility. This observation indicates the superconductivity of Bi4O4S3
to be bulk in nature
Temperature dependence of iron local magnetic moment in phase-separated superconducting chalcogenide
We have studied local magnetic moment and electronic phase separation in
superconducting KFeSe by x-ray emission and absorption
spectroscopy. Detailed temperature dependent measurements at the Fe K-edge have
revealed coexisting electronic phases and their correlation with the transport
properties. By cooling down, the local magnetic moment of Fe shows a sharp drop
across the superconducting transition temperature (T) and the coexisting
phases exchange spectral weights with the low spin state gaining intensity at
the expense of the higher spin state. After annealing the sample across the
iron-vacancy order temperature, the system does not recover the initial state
and the spectral weight anomaly at T as well as superconductivity
disappear. The results clearly underline that the coexistence of the low spin
and high spin phases and the transitions between them provide unusual magnetic
fluctuations and have a fundamental role in the superconducting mechanism of
electronically inhomogeneous KFeSe system.Comment: 6 pages, 5 figure
Influence of substitutional disorder on the electrical transport and the superconducting properties of FeTeSeS
We have carried out an investigation of the structural, magnetic, transport
and superconducting properties of FeTeSeS ceramic
compounds, for and some specific Se (0 x 0.5) and S (0
y 0.12) contents. The incorporation of Se and S to the FeTe
structure produces a progressive reduction of the crystallographic parameters
as well as different degrees of structural disorder associated with the
differences of the ionic radius of the substituting cations. In the present
study, we measure transport properties of this family of compounds and we show
the direct influence of disorder in the normal and superconductor states. We
notice that the structural disorder correlates with a variable range hopping
conducting regime observed at temperatures 200 K. At lower temperatures,
all the samples except the one with the highest degree of disorder show a
crossover to a metallic-like regime, probably related to the transport of
resilient-quasi-particles associated with the proximity of a Fermi liquid state
at temperatures below the superconducting transition. Moreover, the
superconducting properties are depressed only for that particular sample, in
accordance to the condition that superconductivity is affected by disorder when
the electronic localization length becomes smaller than the coherence
length .Comment: 23 pages, 9 figure
Nanoscale phase separation in the iron chalcogenide superconductor K0.8Fe1.6Se2 as seen via scanning nanofocused x-ray diffraction
Advanced synchrotron radiation focusing down to a size of 300 nm has been
used to visualize nanoscale phase separation in the K0.8Fe1.6Se2
superconducting system using scanning nanofocus single-crystal X-ray
diffraction. The results show an intrinsic phase separation in K0.8Fe1.6Se2
single crystals at T< 520 K, revealing coexistence of i) a magnetic phase
characterized by an expanded lattice with superstructures due to Fe vacancy
ordering and ii) a non-magnetic phase with an in-plane compressed lattice. The
spatial distribution of the two phases at 300 K shows a frustrated or arrested
nature of the phase separation. The space-resolved imaging of the phase
separation permitted us to provide a direct evidence of nanophase domains
smaller than 300 nm and different micrometer-sized regions with percolating
magnetic or nonmagnetic domains forming a multiscale complex network of the two
phases.Comment: 5 pages, 4 figure
Points, Walls and Loops in Resonant Oscillatory Media
In an experiment of oscillatory media, domains and walls are formed under the
parametric resonance with a frequency double the natural one. In this bi-stable
system, %phase jumps by crossing walls. a nonequilibrium transition from
Ising wall to Bloch wall consistent with prediction is confirmed
experimentally. The Bloch wall moves in the direction determined by its
chirality with a constant speed. As a new type of moving structure in
two-dimension, a traveling loop consisting of two walls and Neel points is
observed.Comment: 9 pages (revtex format) and 6 figures (PostScript
Effects of Weightlifting Training on Isometric Mid-Thigh Pull Rate of Force Development
PURPOSE: To examine the influence of three distinct training phases on isometric mid-thigh pull (IMTP) measures in well-trained weightlifters. METHODS: Pre- and post-block IMTP data from 11 collegiate weightlifters was used for analysis. The mean of the best two attempts from each athlete for measures of PF and RFD from 0-50ms, 0-100ms, 0-150ms, 0-200ms, and 0-250ms were used for comparison. In total, results from five timepoints for each of the 11 athletes were examined in order to compare the effects of the three training phases. RESULTS: A repeated measures ANOVA revealed no statistically significant (p ≥ 0.05) effects of training on any of the variables measured. When comparing post block values from each phase to pre-training cycle values, the largest increase in RFD200 (d = 0.22) and RFD250 (d=0.22) occurred post strength-power (SP) phase, while the peak in RFD50 (d = 0.32), RFD100 (d = 0.31), and RFD150 (d = 0.22) occurred after the peak/taper (PT) phase. CONCLUSIONS: Based on the results of the study, it is possible that changes in IMTP RFD may reflect the expected adaptations of block periodization. Rather than examining RFD changes at only one time-band, it may be valuable to monitor RFD across multiple time bands as changes in early and late RFD may not occur proportionally during a peak/taper phase
Superconductivity at 27 K in tetragonal FeSe under high pressure
A huge enhancement of the superconducting transition temperature Tc was
observed in tetragonal FeSe superconductor under high pressure. The onset
temperature became as high as 27 K at 1.48 GPa and the pressure coefficient
showed a huge value of 9.1 K/GPa. The upper critical field Hc2 was estimated to
be ~ 72 T at 1.48 GPa. Because of the high Hc2, FeSe system may be a candidate
for application as superconducting wire rods. Moreover, the investigation of
superconductivity on simple structured FeSe may provide important clues to the
mechanism of superconductivity in iron-based superconductors.Comment: 8 pages, 6 figure
s-wave pairing in the optimally-doped LaO0.5F0.5BiS2 superconductor
We report on the magnetic and superconducting properties of LaO0.5F0.5BiS2 by
means of zero- (ZF) and transverse-field (TF) muon-spin spectroscopy
measurements (uSR). Contrary to previous results on iron-based superconductors,
measurements in zero field demonstrate the absence of magnetically ordered
phases. TF-uSR data give access to the superfluid density, which shows a marked
2D character with a dominant s-wave temperature behavior. The field dependence
of the magnetic penetration depth confirms this finding and further suggests
the presence of an anisotropic superconducting gap
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