31 research outputs found
Low-energy spin excitations in optimally doped CaFeCoAsF superconductor studied with inelastic neutron scattering
There are few inelastic neutron scattering (INS) reports on the
superconducting single crystals of FeAs-1111 system, even though it was first
discovered in 2008, due to the extreme difficulty in large single crystal
growth. In this paper, we have studied the low-energy spin excitations in the
optimally electron-doped CaFeCoAsF single crystals with
= 21 K by INS. The resonance energy of the superconducting spin
resonant mode with = 12 meV amounts to 6.6
, which constitutes the largest
/ ratio among iron-based
superconductors reported to date. The large ratio implies a strong coupling
between conduction electrons and magnetic excitations in
CaFeCoAsF. The resonance possesses a magnonlike upward
dispersion along transverse direction due to the anisotropy of spin-spin
correlation length within plane in the normal-state, which points to a
spin fluctuation mediated sign-reversed wave pairing in
CaFeCoAsF
Coexistence of ferromagnetism, antiferromagnetism, and superconductivity in magnetically anisotropic (Eu,La)FeAs2
Materials with exceptional magnetism and superconductivity usually conceive
emergent physical phenomena. Here, we investigate the physical properties of
the (Eu,La)FeAs2 system with double magnetic sublattices. The parent EuFeAs2
shows anisotropy-associated magnetic behaviors, such as Eu-related moment
canting and exchange bias. Through La doping, the magnetic anisotropy is
enhanced with ferromagnetism of Eu2+ realized in the overdoped region, and a
special exchange bias of the superposed ferromagnetic/superconducting loop
revealed in Eu0.8La0.2FeAs2. Meanwhile, the Fe-related antiferromagnetism shows
unusual robustness against La doping. Theoretical calculation and 57Fe
M\"ossbauer spectroscopy investigation reveal a doping-tunable dual
itinerant/localized nature of the Fe-related antiferromagnetism. Coexistence of
the Eu-related ferromagnetism, Fe-related robust antiferromagnetism, and
superconductivity is further revealed in Eu0.8La0.2FeAs2, providing a platform
for further exploration of potential applications and emergent physics.
Finally, an electronic phase diagram is established for (Eu,La)FeAs2 with the
whole superconducting dome adjacent to the Fe-related antiferromagnetic phase,
which is of benefit for seeking underlying clues to high-temperature
superconductivity.Comment: 13 pages, 6 figures for the main tex
Growth of millimeter-sized high-quality CuFeSe single crystals by the molten salt method and study of their semiconducting behavior
An eutectic AlCl/KCl molten salt method in a horizontal configuration was
employed to grow millimeter-sized and composition homogeneous CuFeSe single
crystals due to the continuous growth process in a temperature gradient induced
solution convection. The typical as-grown CuFeSe single crystals in cubic
forms are nearly 1.61.21.0 mm3 in size. The chemical
composition and homogeneity of the crystals was examined by both inductively
coupled plasma atomic emission spectroscopy and energy dispersive spectrometer
with Cu:Fe:Se = 0.96:1.00:1.99 consistent with the stoichiometric composition
of CuFeSe. The magnetic measurements suggest a ferrimagnetic or weak
ferromagnetic transition below T = 146 K and the resistivity reveals a
semiconducting behavior and an abrupt increase below T
Superconductivity in a new layered cobalt oxychalcogenide NaCoSeO with a 3 triangular lattice
Unconventional superconductivity in bulk materials under ambient pressure is
extremely rare among the 3 transition-metal compounds outside the layered
cuprates and iron-based family. It is predominantly linked to highly
anisotropic electronic properties and quasi-two-dimensional (2D) Fermi
surfaces. To date, the only known example of the Co-based exotic superconductor
was the hydrated layered cobaltate, NaCoO yHO, and its
superconductivity is realized in the vicinity of a spin-1/2 Mott state.
However, the nature of the superconductivity in these materials is still an
active subject of debate, and therefore, finding new class of superconductors
will help unravel the mysteries of their unconventional superconductivity. Here
we report the discovery of unconventional superconductivity at 6.3 K in
our newly synthesized layered compound NaCoSeO, in
which the edge-shared CoSe octahedra form [CoSe] layers with a
perfect triangular lattice of Co ions. It is the first 3 transition-metal
oxychalcogenide superconductor with distinct structural and chemical
characteristics. Despite its relatively low , material exhibits
extremely high superconducting upper critical fields, , which
far exceeds the Pauli paramagnetic limit by a factor of 3 - 4. First-principles
calculations show that NaCoSeO is a rare example of
negative charge transfer superconductor. This new cobalt oxychalcogenide with a
geometrical frustration among Co spins, shows great potential as a highly
appealing candidate for the realization of high- and/or unconventional
superconductivity beyond the well-established Cu- and Fe-based superconductor
families, and opened a new field in physics and chemistry of low-dimensional
superconductors
The relationship between depressive and anxious symptoms and school attendance among adolescents seeking psychological services in a public general hospital in China: a cross-sectional study
Abstract Background School attendance problems (SAPs), whether absenteeism or dropout, are strongly associated with poor outcomes for adolescents. We examined multiple variables that influence SAPs to identify potential leverage points for improving school attendance. Methods Self-reported SAPs and demographic information was collected from 392 adolescents in adolescents presenting to the general hospital for psychological services. PHQ-9 and GAD-7 were applied to assess the severity of depressive and anxious symptoms. We constructed logistic regression analysis and the Chi-Square Automatic Interaction Detection (CHAID) segmentation analysis via SPSS Decision Tree to identifying risk factors for the development of SAPs in adolescents. Results SAPs were self-reported by 252 (64.3%) adolescents. The SAPs group and non-SAPs group showed a significant difference in age, PHQ9 total scores, GAD7 total scores, schools, siblings, residence, parental marital quality, general health, regular exercise, and regular diet. A post hoc comparison between the two groups showed that the frequency of SAPs was significantly higher in the moderately-severe and severe depressive groups compared with other three groups (none, mild, moderate). The frequency of SAPs in severe anxious groups was significantly different from the none-anxious group. According to the binary logistic regression analysis, the depressive severity, siblings, residence, marital quality of parents, general health, and regular diet were correlated with the SAPs among adolescents. The adjusted OR of SAPs according to moderately-severe depressive symptoms was 10.84 (95%CI: 1.967–59.742) and severe depressive symptoms was 6.659 (95%CI: 1.147–38.666). In the decision tree model, PHQ-9 severity was extracted as the first splitting variable, with regular exercise and residence as the second, and siblings as the third. The ROC curves for predicting SAPs showed a fair diagnostic accuracy of the model with AUCs of CHAID model (0.705,95%CI:0.652–0.759, P = 0.000) and logistic regression model (0.777,95%CI:0.729–0.824, P = 0.000). Conclusion Our study provides insights into the associations between depressive symptoms and poor school attendance and identifies a number of risk factors associated with SAPs. Effective intervention by mental health practitioners, more attention by policy makers, and further research in this area are urgently needed for adolescents