58 research outputs found
Electron doping evolution of the magnetic excitations in BaFe2-xNixAs2
We use inelastic neutron scattering (INS) spectroscopy to study the magnetic
excitations spectra throughout the Brioullion zone in electron-doped iron
pnictide superconductors BaFeNiAs with .
While the sample is near optimal superconductivity with K
and has coexisting static incommensurate magnetic order, the
samples are electron-overdoped with reduced of 14 K and 8 K,
respectively, and have no static antiferromagnetic (AF) order. In previous INS
work on undoped () and electron optimally doped () samples, the
effect of electron-doping was found to modify spin waves in the parent compound
BaFeAs below 100 meV and induce a neutron spin resonance at the
commensurate AF ordering wave vector that couples with superconductivity. While
the new data collected on the sample confirms the overall features of
the earlier work, our careful temperature dependent study of the resonance
reveals that the resonance suddenly changes its -width below similar
to that of the optimally hole-doped iron pnictides
BaKFeAs. In addition, we establish the dispersion of
the resonance and find it to change from commensurate to transversely
incommensurate with increasing energy. Upon further electron-doping to
overdoped iron pnictides with and 0.18, the resonance becomes weaker
and transversely incommensurate at all energies, while spin excitations above
100 meV are still not much affected. Our absolute spin excitation
intensity measurements throughout the Brillouin zone for
confirm the notion that the low-energy spin excitation coupling with itinerant
electron is important for superconductivity in these materials, even though the
high-energy spin excitations are weakly doping dependent.Comment: 16 pages, 16 figure
Electron doping evolution of the anisotropic spin excitations in BaFe2-xNixAs2
We use inelastic neutron scattering to systematically investigate the
Ni-doping evolution of the low-energy spin excitations in BaFe2-xNixAs2
spanning from underdoped antiferromagnet to overdoped superconductor (0.03< x <
0.18). In the undoped state, the low-energy (<80 meV) spin waves of BaFe2As2
form transversely elongated ellipses in the [H, K] plane of the reciprocal
space. Upon Ni-doping, the c-axis magnetic exchange coupling is rapidly
suppressed and the momentum distribution of spin excitations in the [H, K]
plane is enlarged in both the transverse and longitudinal directions with
respect to the in-plane AF ordering wave vector of the parent compound. As a
function of increasing Ni-doping x, the spin excitation widths increase
linearly but with a larger rate along the transverse direction. These results
are in general agreement with calculations of dynamic susceptibility based on
the random phase approximation (RPA) in an itinerant electron picture. For
samples near optimal superconductivity at x= 0.1, a neutron spin resonance
appears in the superconducting state. Upon further increasing the
electron-doping to decrease the superconducting transition temperature Tc, the
intensity of the low-energy magnetic scattering decreases and vanishes
concurrently with vanishing superconductivity in the overdoped side of the
superconducting dome. Comparing with the low-energy spin excitations centered
at commensurate AF positions for underdoped and optimally doped materials
(x<0.1), spin excitations in the over-doped side (x=0.15) form transversely
incommensurate spin excitations, consistent with the RPA calculation.
Therefore, the itinerant electron approach provides a reasonable description to
the low-energy AF spin excitations in BaFe2-xNixAs2.Comment: 11 pages, 11 figure
Quantum Spin Excitations through the metal-to-insulator crossover in
We use inelastic neutron scattering to study the temperature dependence of
the spin excitations of a detwinned superconducting YBaCuO
( K). In contrast to earlier work on YBaCuO (
K), where the prominent features in the magnetic spectra consist of a sharp
collective magnetic excitation termed ``resonance'' and a large
( meV) superconducting spin gap, we find that the spin
excitations in YBaCuO are gapless and have a much broader
resonance. Our detailed mapping of magnetic scattering along the
/-axis directions at different energies reveals that spin
excitations are unisotropic and consistent with the ``hourglass''-like
dispersion along the -axis direction near the resonance, but they are
isotropic at lower energies. Since a fundamental change in the low-temperature
normal state of YBaCuO when superconductivity is suppressed
takes place at with a metal-to-insulator crossover (MIC), where the
ground state transforms from a metallic to an insulating-like phase, our
results suggest a clear connection between the large change in spin excitations
and the MIC. The resonance therefore is a fundamental feature of metallic
ground state superconductors and a consequence of high- superconductivity.Comment: 9 pages, 7 figures, accepted by Phys. Rev.
Students’ Perception toward Elements of Globalization in Four Interdisciplinary Summer Schools in Shiraz University of Medical Sciences in Iran
Background & Objective: Globalization is one of the most important topics in higher education today, which presents a powerful challenge and an opportunity for medical sciences university and healthcare provider. Nowadays, increasingly faced with healthcare challenges that require an understanding of global health trends and practices, yet little is known about what constitutes appropriate global health training. The main purpose of this research was to review the association between perception of globalization and information mastery and curriculum planning.
Methods: This was a descriptive-analytical study on medical students. The study population consisted of 180 medical sciences students who were selected with random sampling methods. In order to measure attitudes of students towards globalization, measures were developed and used by researchers. For the purpose of evaluating of the validity of the measures, construct validity was utilized by factor analysis. In order to determine the reliability of the measures Cronbach's alpha was used, as well.
Results: Findings indicated that the total respondents agreed or had positive approach towards globalization. Based on the results of the factor analysis, four factors i.e. personal and social attitude with 15 questions, sociopolitical attitude, and 7 question, two questions for performance and the fourth factor was the resource management concept of globalization which were identified with only one question in the questionnaire. Analysis of variance (ANOVA) results showed that there was no statistically significant association the students' perspective and demographic variables gender, school and age.
Conclusion: The positive perception of globalization highlighted the needs of global health educational competencies and approaches used in medical schools and the need to facilitate greater consensus amongst medical educators and students on appropriate global health training for future health care providers. This process led to world integration, density of human awareness and world culture formation
Keywords
Globalization Medical sciences students Factor analysi
Dynamic spin-lattice coupling and nematic fluctuations in NaFeAs
We use inelastic neutron scattering to study acoustic phonons and spin
excitations in single crystals of NaFeAs, a parent compound of iron pnictide
superconductors. NaFeAs exhibits a tetragonal-to-orthorhombic structural
transition at K and a collinear antiferromagnetic (AF) order at
K. While longitudinal and out-of-plane transverse acoustic
phonons behave as expected, the in-plane transverse acoustic phonons reveal
considerable softening on cooling to , and then harden on approaching
before saturating below . In addition, we find that spin-spin
correlation lengths of low-energy magnetic excitations within the FeAs layer
and along the -axis increase dramatically below , and show weak anomaly
across . These results suggest that the electronic nematic phase present
in the paramagnetic tetragonal phase is closely associated with dynamic
spin-lattice coupling, possibly arising from the one-phonon-two-magnon
mechanism
High-energy magnetic excitations from heavy quasiparticles in CeCuSi
Magnetic fluctuations is the leading candidate for pairing in cuprate,
iron-based and heavy fermion superconductors. This view is challenged by the
recent discovery of nodeless superconductivity in CeCuSi, and calls for
a detailed understanding of the corresponding magnetic fluctuations. Here, we
mapped out the magnetic excitations in \ys{superconducting (S-type)}
CeCuSi using inelastic neutron scattering, finding a strongly
asymmetric dispersion for ~meV, which at higher energies evolve
into broad columnar magnetic excitations that extend to meV. While
low-energy magnetic excitations exhibit marked three-dimensional
characteristics, the high-energy magnetic excitations in CeCuSi are
almost two-dimensional, reminiscent of paramagnons found in cuprate and
iron-based superconductors. By comparing our experimental findings with
calculations in the random-phase approximation,we find that the magnetic
excitations in CeCuSi arise from quasiparticles associated with its
heavy electron band, which are also responsible for superconductivity. Our
results provide a basis for understanding magnetism and superconductivity in
CeCuSi, and demonstrate the utility of neutron scattering in probing
band renormalization in heavy fermion metals
A Mott insulator continuously connected to iron pnictide superconductors
Iron-based superconductivity develops near an antiferromagnetic order and out
of a bad metal normal state, which has been interpreted as originating from a
proximate Mott transition. Whether an actual Mott insulator can be realized in
the phase diagram of the iron pnictides remains an open question. Here we use
transport, transmission electron microscopy, X-ray absorption spectroscopy, and
neutron scattering to demonstrate that NaFeCuAs near
exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators
with the insulating behavior persisting above the N\'eel temperature,
indicative of a Mott insulator. Upon decreasing from , the
antiferromagnetic ordered moment continuously decreases, yielding to
superconductivity around . Our discovery of a Mott insulating state in
NaFeCuAs thus makes it the only known Fe-based material in which
superconductivity can be smoothly connected to the Mott insulating state,
highlighting the important role of electron correlations in the high- superconductivity.Comment: in press, Nat. Commun., 4 figures, supplementary information
available upon reques
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