3,186 research outputs found
Emergent phases in iron pnictides: Double-Q antiferromagnetism, charge order and enhanced nematic correlations
Electron correlations produce a rich phase diagram in the iron pnictides.
Earlier theoretical studies on the correlation effect demonstrated how quantum
fluctuations weaken and concurrently suppress a -symmetric single-Q
antiferromagnetic order and a nematic order. Here we examine the emergent
phases near the quantum phase transition. For a -symmetric collinear
double-Q antiferromagnetic order, we show that it is accompanied by both a
charge order and an enhanced nematic susceptibility. Our results provide
understanding for several intriguing recent experiments in hole-doped iron
arsenides, and bring out common physics that underlies the different magnetic
phases of various iron-based superconductors.Comment: 5+6 pages, 2 figures; (v2) issues with cross-referencing between the
main text and supplementary material are fixe
Local orthorhombicity in the magnetic phase of the hole-doped iron-arsenide superconductor SrNaFeAs
We report temperature-dependent pair distribution function measurements of
SrNaFeAs, an iron-based superconductor system that
contains a magnetic phase with reentrant tetragonal symmetry, known as the
magnetic phase. Quantitative refinements indicate that the instantaneous
local structure in the phase is comprised of fluctuating orthorhombic
regions with a length scale of 2 nm, despite the tetragonal symmetry of
the average static structure. Additionally, local orthorhombic fluctuations
exist on a similar length scale at temperatures well into the paramagnetic
tetragonal phase. These results highlight the exceptionally large nematic
susceptibility of iron-based superconductors and have significant implications
for the magnetic phase and the neighboring and superconducting
phases
The Nematic Energy Scale and the Missing Electron Pocket in FeSe
Superconductivity emerges in proximity to a nematic phase in most iron-based
superconductors. It is therefore important to understand the impact of
nematicity on the electronic structure. Orbital assignment and tracking across
the nematic phase transition prove to be challenging due to the multiband
nature of iron-based superconductors and twinning effects. Here, we report a
detailed study of the electronic structure of fully detwinned FeSe across the
nematic phase transition using angle-resolved photoemission spectroscopy. We
clearly observe a nematicity-driven band reconstruction involving dxz, dyz, and
dxy orbitals. The nematic energy scale between dxz and dyz bands reaches a
maximum of 50 meV at the Brillouin zone corner. We are also able to track the
dxz electron pocket across the nematic transition and explain its absence in
the nematic state. Our comprehensive data of the electronic structure provide
an accurate basis for theoretical models of the superconducting pairing in
FeSe
Observation of Temperature-Induced Crossover to an Orbital-Selective Mott Phase in AFeSe (A=K, Rb) Superconductors
In this work, we study the AFeSe (A=K, Rb) superconductors
using angle-resolved photoemission spectroscopy. In the low temperature state,
we observe an orbital-dependent renormalization for the bands near the Fermi
level in which the dxy bands are heavily renormliazed compared to the dxz/dyz
bands. Upon increasing temperature to above 150K, the system evolves into a
state in which the dxy bands have diminished spectral weight while the dxz/dyz
bands remain metallic. Combined with theoretical calculations, our observations
can be consistently understood as a temperature induced crossover from a
metallic state at low temperature to an orbital-selective Mott phase (OSMP) at
high temperatures. Furthermore, the fact that the superconducting state of
AFeSe is near the boundary of such an OSMP constraints the
system to have sufficiently strong on-site Coulomb interactions and Hund's
coupling, and hence highlight the non-trivial role of electron correlation in
this family of iron superconductors
Nematic spin correlations pervading the phase diagram of FeSeS
We use resonant inelastic X-ray scattering (RIXS) at the Fe-L edge to
study the spin excitations of uniaxial-strained and unstrained
FeSeS () samples. The measurements on unstrained
samples reveal dispersive spin excitations in all doping levels, which show
only minor doping dependence in energy dispersion, lifetime, and intensity,
indicating that high-energy spin excitations are only marginally affected by
sulfur doping. RIXS measurements on uniaxial-strained samples reveal that the
high-energy spin-excitation anisotropy observed previously in FeSe is also
present in the doping range of FeSeS. The
spin-excitation anisotropy persists to a high temperature up to K in
and reaches a maximum around the nematic quantum critical doping
(). Since the spin-excitation anisotropy directly reflects the
existence of nematic spin correlations, our results indicate that high-energy
nematic spin correlations pervade the regime of nematicity in the phase diagram
and are enhanced by the nematic quantum criticality. These results emphasize
the essential role of spin fluctuations in driving electronic nematicity and
open the door for uniaxial strain tuning of spin excitations in quantum
materials hosting strong magnetoelastic coupling and electronic nematicity.Comment: 6 pages, 4 figures, supplemental materials uploade
Capacitive coupling study of the HERD SCD prototype: preliminary results
The Silicon Charge Detector (SCD) is a subdetector of the High Energy Cosmic
Radiation Detection payload. The dynamic range of the silicon microstrip
detector can be extended by the capacitive coupling effect, which is related to
the interstrip capacitance and the coupling capacitance. A detector prototype
with several sets of parameters was designed and tested in the ion beams at the
CERN Super Proton Synchrotron. The capacitive coupling fractions with readout
strip and floating strip incidences were studied using the beam test data and
SPICE simulation
Traditional Chinese medicine for smoking cessation: An umbrella review of systematic reviews and meta-analysis of randomized controlled trials.
Traditional Chinese medicine (TCM) may have special advantages in facilitating smoking cessation, but consensus on effectiveness is lacking. We aim to comprehensively review, update, and refine current evidence on TCM effectiveness and safety. Nine databases were searched from their inception up to 28 February 2023. Systematic reviews (SRs) and meta-analysis of TCM for smoking cessation were identified and retrieved. Additional databases and hand searches of RCTs from included SRs were performed for data pooling. Cochrane ROB tools and AMSTAR-2 were used to evaluate the methodological quality of RCTs and SRs, respectively. RCT data are presented as relative risks (RR) or mean differences (MD) with 95% confidence intervals (CI) using RevMan 5.4. Thirteen SRs involving 265 studies with 33081 participants were included. Among these 265 studies, 157 were duplicates (58.36%) and 52 were non-RCTs (19.62%). Combined with the remaining 56 RCTs identified through hand searches, 88 RCTs involving 12434 participants were finally included for data synthesis. All the SRs focused on acupoint stimulation, and the majority were of low or very low quality. The methodological quality of RCTs was either unclear or high risk. For continuous abstinence rate, TCM external interventions were better than placebo in 6 months to 1 year (RR=1.60; 95% CI: 1.14-2.25; I =27%; n=5533 participants). Compared with placebo, TCM external application was effective in reducing nicotine withdrawal symptoms, and the effect was gradually stable and obvious in the fourth week (MD= -4.46; 95% CI: -5.43 - -3.49; n=165 participants). Twelve RCTs reported adverse events as outcome indicators for safety evaluation, and no serious adverse events occurred. Despite the methodological limitations of the original studies, our review suggests that TCM intervention shows potential effectiveness on the continuous abstinence rate. Extending the intervention time can enhance the effect of TCM on nicotine withdrawal symptoms. Referred to adverse events, more data for safety evaluation are required. [Abstract copyright: Β© 2023 Lu CL. et al.
Tag SNP Polymorphism of CCL2 and Its Role in Clinical Tuberculosis in Han Chinese Pediatric Population
BACKGROUND: Chemokine (C-C motif) ligand 2 CCL2/MCP-1 is among the key signaling molecules of innate immunity; in particular, it is involved in recruitment of mononuclear and other cells in response to infection, including tuberculosis (TB) and is essential for granuloma formation. METHODOLOGY/PRINCIPAL FINDINGS: We identified a tag SNP for the CCL2/MCP-1 gene (rs4586 C/T). In order to understand whether this SNP may serve to evaluate the contribution of the CCL2 gene to the expression of TB disease, we further analysed distribution of its alleles and genotypes in 301 TB cases versus 338 non-infected controls (all BCG vaccinated) representing a high-risk pediatric population of North China. In the male TB subgroup, the C allele was identified in a higher rate (Pβ=β0.045), and, acting dominantly, was found to be a risk factor for clinical TB (Pβ=β0.029). Homozygous TT genotype was significantly associated with lower CSF mononuclear leukocyte (ML) counts in patients with tuberculous meningitis (TBM) (Pβ=β0.001). CONCLUSIONS/SIGNIFICANCE: The present study found an association of the CCL2 tag SNP rs4586 C allele and pediatric TB disease in males, suggesting that gender may affect the susceptibility to TB even in children. The association of homozygous TT genotype with decreased CSF mononuclear leukocyte (ML) count not only suggests a clinical significance of this SNP, but indicates its potential to assist in the clinical assessment of suspected TBM, where delay is critical and diagnosis is difficult
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