48 research outputs found
Multiband superconductivity and a deep gap minimum evidenced by specific heat in KCa(FeNi)AsF
Specific heat can explore low-energy quasiparticle excitations of
superconductors, so it is a powerful tool for bulk measurement on the
superconducting gap structure and pairing symmetry. Here, we report an in-depth
investigation on the specific heat of the multiband superconductors
KCa(FeNi)AsF ( = 0, 0.05, 0.13) single crystals
and the overdoped non-superconducting one with = 0.17. For the samples with
= 0 and = 0.05, the magnetic field induced specific heat coefficient
in the low temperature limit increases rapidly below 2 T,
then it rises slowly above 2 T. Using the non-superconducting sample with =
0.17 as a reference, and applying a mixed model that combines Debye and
Einstein modes, the specific heat of phonon background for various
superconducting samples can be fitted and the detailed information of the
electronic specific heat is obtained. Through comparative analyses, it is found
that the energy gap structure including two -wave gaps and an extended
-wave gap with large anisotropy can reasonably describe the electronic
specific heat data. According to these results, we suggest that at least one
anisotropic superconducting gap with a deep gap minimum should exist in this
multiband system. With the doping of Ni, the of the sample decreases
along with the decrease of the large -wave gap, but the extended -wave
gap increases due to the enlarged electron pockets via adding more electrons.
Despite these changes, the general properties of the gap structure remain
unchanged versus doping Ni. In addition, the calculation of condensation energy
of the parent and doped samples shows the rough consistency with the
correlation of with = 3-4, which is beyond the
understanding of the BCS theory
Assessing the causal relationship between genetically determined inflammatory biomarkers and low back pain risk: a bidirectional two-sample Mendelian randomization study
BackgroundObservational studies have suggested an association between inflammatory markers and low back pain (LBP), but the causal relationship between these factors remains uncertain.MethodsWe conducted a bidirectional two-sample Mendelian randomization analysis (MR) study to investigate whether there is a causal relationship between inflammatory markers and low back pain. We obtained genetic data for CRP, along with its upstream inflammatory markers IL-6, IL-8, and IL-10, as well as low back pain from publicly available genome-wide association studies (GWAS). We applied several MR methods, including inverse variance weighting, weighted median, MR-Egger, Wald Ratio, and MR-PRESSO, to test for causal relationships. Sensitivity analyses were also conducted to assess the robustness of the results.ResultsOur analyses utilizing the Inverse Variance Weighted (IVW) method, the MR-Egger method, and the weighted median method indicated that IL-6 may be associated with an increased risk of LBP (Effect Size: -0.009, 95% Confidence Interval: -0.013–0.006, p = 9.16e-08); however, in the reverse direction, there was no significant causal effect of LBP on inflammatory markers.ConclusionOur study used a Mendelian randomization approach and found that elevated IL-6 levels may reduce the risk of LBP
Nodal s± pairing symmetry in an iron-based superconductor with only hole pockets
The origin of high-temperature superconductivity in iron-based superconductors is still not understood; determination of the pairing symmetry is essential for understanding the superconductivity mechanism. In the iron-based superconductors that have hole pockets around the Brillouin zone centre and electron pockets around the zone corners, the pairing symmetry is generally considered to be s±, which indicates a sign change in the superconducting gap between the hole and electron pockets. For the iron-based superconductors with only hole pockets, however, a couple of pairing scenarios have been proposed, but the exact symmetry is still controversial. Here we determine that the pairing symmetry in KFe2As2—which is a prototypical iron-based superconductor with hole pockets both around the zone centre and around the zone corners—is also of the s± type. Our laser-based angle-resolved photoemission measurements have determined the superconducting gap distribution and identified the locations of the gap nodes on all the Fermi surfaces around the zone centres and the zone corners. These results unify the pairing symmetry in hole-doped iron-based superconductors and point to spin fluctuation as the pairing glue in generating superconductivity
Extreme suppression of antiferromagnetic order and critical scaling in a two-dimensional random quantum magnet
Sr_2CuTeO_6 is a square-lattice Néel antiferromagnet with superexchange between first-neighbor S=1/2 Cu spins mediated by plaquette centered Te ions. Substituting Te by W, the affected impurity plaquettes have predominantly second-neighbor interactions, thus causing local magnetic frustration. Here we report a study of Sr_2CuTe_1-xW_xO_6 using neutron diffraction and μSR techniques, showing that the Néel order vanishes already at x=0.025±0.005. We explain this extreme order suppression using a two-dimensional Heisenberg spin model, demonstrating that a W-type impurity induces a deformation of the order parameter that decays with distance as 1/r^2 at temperature T=0. The associated logarithmic singularity leads to loss of order for any x>0. Order for small x>0 and T>0 is induced by weak interplane couplings. In the nonmagnetic phase of Sr_2CuTe_1-x W_x O_6, the μSR relaxation rate exhibits quantum critical scaling with a large dynamic exponent, z≈3, consistent with a random-singlet state.Accepted manuscrip