85 research outputs found
Neutron scattering sum rules, symmetric exchanges, and helicoidal magnetism in MnSb2O6
MnSb2O6 is based on the noncentrosymmetric P321 space group with magnetic Mn2+ (S=5/2, L≈0) spins ordering below TN=12K in a cycloidal structure. The spin rotation plane was found to be tilted away from the c axis [Kinoshita, Phys. Rev. Lett. 117, 047201 (2016)10.1103/PhysRevLett.117.047201] resulting as a helicoidal ground state, which we refer as the tilted structure. In our previous diffraction study [Chan, Phys. Rev. B 106, 064403 (2022)10.1103/PhysRevB.106.064403] we found no evidence that this tilted structure is favored over the pure cycloidal order (referred as the untilted structure). The ground-state magnetic structure, expected to be built and originate from seven nearest-neighbor Heisenberg exchange constants, has been shown to be coupled to the underlying crystallographic chirality with polar domain switching being reported. We apply neutron spectroscopy to extract these symmetric exchange constants. Given the high complexity of the magnetic exchange network, crystallographic structure and complications fitting many parameter linear spin-wave models, we take advantage of multiplexed neutron instrumentation to use the first moment sum rule of neutron scattering to estimate these symmetric exchange constants. The first moment of neutron scattering provides a way of deriving the Heisenberg exchange constant between two neighboring spins if the relative angle and distance of the two ordered spins is known. We show that the first moment sum rule combined with the known magnetic ordering wavevector fixes six of the seven exchange constants. The remaining exchange constant is not determined by this analysis because of the equal spatial bond distances present for different chiral exchange interactions. However, we find this parameter is fixed by the magnon dispersion near the magnetic zone boundary, which is not sensitive to the tilting of the global magnetic structure. We then use these parameters to calculate the low-energy spin-waves in the Néel state to reproduce the neutron response without strong antisymmetric coupling. Using Green's response functions, the stability of long-wavelength excitations in the context of our proposed untilted magnetic structures is then discussed. The results show the presence of strong symmetric exchange constants for the chiral exchange pathways and illustrate an underlying coupling between crystallographic and magnetic "chirality"through predominantly symmetric exchange. We further argue that the excitations can be consistently modelled in terms of an untilted magnetic structure in the presence of symmetric-only exchange constants
Animal products, calcium and protein and prostate cancer risk in the Netherlands Cohort Study
Prostate cancer risk in relation to consumption of animal products, and intake of calcium and protein was investigated in the Netherlands Cohort Study. At baseline in 1986, 58,279 men aged 55-69 years completed a self-administered 150-item food frequency questionnaire and a questionnaire on other risk factors for cancer. After 6.3 years of follow-up, 642 prostate cancer cases were available for analysis. In multivariate case-cohort analyses adjusted for age, family history of prostate cancer and socioeconomic status, no associations were found for consumption of fresh meat, fish, cheese and eggs. Positive trends in risk were found for consumption of cured meat and milk products (P-values 0.04 and 0.02 respectively). For calcium and protein intake, no associations were observed. The hypothesis that dietary factors might be more strongly related to advanced prostate rumours could not be confirmed in our study. We conclude that, in this study, animal products are not strongly related to prostate cancer risk
Magnetism and its microscopic origin in iron-based high-temperature superconductors
High-temperature superconductivity in the iron-based materials emerges from,
or sometimes coexists with, their metallic or insulating parent compound
states. This is surprising since these undoped states display dramatically
different antiferromagnetic (AF) spin arrangements and Nel
temperatures. Although there is general consensus that magnetic interactions
are important for superconductivity, much is still unknown concerning the
microscopic origin of the magnetic states. In this review, progress in this
area is summarized, focusing on recent experimental and theoretical results and
discussing their microscopic implications. It is concluded that the parent
compounds are in a state that is more complex than implied by a simple Fermi
surface nesting scenario, and a dual description including both itinerant and
localized degrees of freedom is needed to properly describe these fascinating
materials.Comment: 14 pages, 4 figures, Review article, accepted for publication in
Nature Physic
A Large Iron Isotope Effect in SmFeAsO1-xFx and Ba1-xKxFe2As2
The recent discovery of superconductivity in oxypnictides with the critical
temperature (TC) higher than McMillan limit of 39 K (the theoretical maximum
predicted by Bardeen-Cooper-Schrieffer (BCS) theory) has generated great
excitement. Theoretical calculations indicate that the electron-phonon
interaction is not strong enough to give rise to such high transition
temperatures, while strong ferromagnetic/antiferromagnetic fluctuations have
been proposed to be responsible. However, superconductivity and magnetism in
pnictide superconductors show a strong sensitivity to the lattice, suggesting a
possibility of unconventional electron-phonon coupling. Here we report the
effect of oxygen and iron isotopic mass on Tc and the spin-density wave (SDW)
transition temperature (TSDW) in SmFeAsO1-xFx and Ba1-xKxFe2As2 systems. The
results show that oxygen isotope effect on TC and TSDW is very little, while
the iron isotope exponent alpha=-dlnTc/dlnM is about 0.35, being comparable to
0.5 for the full isotope effect. Surprisingly, the iron isotope exchange shows
the same effect on TSDW as TCc These results indicate that electron-phonon
interaction plays some role in the superconducting mechanism, but simple
electron-phonon coupling mechanism seems to be rather unlikely because a strong
magnon-phonon coupling is included. Sorting out the interplay between the
lattice and magnetic degrees of freedom is a key challenge for understanding
the mechanism of high-TC superconductivity.Comment: 22 pages, 7 figur
Prostate cancer risk and consumption of fish oils: a dietary biomarker-based case–control study
Experimental studies suggest that the risk of prostate cancer is reduced with the intake of long-chain n-3 polyunsaturated fatty acids derived from marine foods, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). However, few human studies have been conducted due to difficulties in assessing the dietary intake of these fatty acids. The authors examined the relationship between prostate cancer risk and EPA and DHA in erythrocyte biomarkers in a population-based case–control study in Auckland, New Zealand during 1996–1997 involving 317 prostate cancer cases and 480 age-matched community controls. Reduced prostate cancer risk was associated with high erythrocyte phosphatidylcholine levels of EPA (multivariate relative risk = 0.59; 95% confidence interval 0.37–0.95, upper vs lowest quartile) and DHA (multivariate relative risk = 0.62; 95% confidence interval 0.39–0.98, upper vs lowest quartile). These analyses support evidence from in vitro experiments for a reduced risk of prostate cancer associated with dietary fish oils, possibly acting via inhibition of arachidonic acid-derived eicosanoid biosynthesis. © 1999 Cancer Research Campaig
Experimental signatures of emergent quantum electrodynamics in PrHfO
In a quantum spin liquid, the magnetic moments of the constituent electron
spins evade classical long-range order to form an exotic state that is quantum
entangled and coherent over macroscopic length scales [1-2]. Such phases offer
promising perspectives for device applications in quantum information
technologies, and their study can reveal fundamentally novel physics in quantum
matter. Quantum spin ice is an appealing proposal of one such state, in which
the fundamental ground state properties and excitations are described by an
emergent U(1) lattice gauge theory [3-7]. This quantum-coherent regime has
quasiparticles that are predicted to behave like magnetic and electric
monopoles, along with a gauge boson playing the role of an artificial photon.
However, this emergent lattice quantum electrodynamics has proved elusive in
experiments. Here we report neutron scattering measurements of the rare-earth
pyrochlore magnet PrHfO that provide evidence for a quantum spin
ice ground state. We find a quasi-elastic structure factor with pinch points -
a signature of a classical spin ice - that are partially suppressed, as
expected in the quantum-coherent regime of the lattice field theory at finite
temperature. Our result allows an estimate for the speed of light associated
with magnetic photon excitations. We also reveal a continuum of inelastic spin
excitations, which resemble predictions for the fractionalized, topological
excitations of a quantum spin ice. Taken together, these two signatures suggest
that the low-energy physics of PrHfO can be described by emergent
quantum electrodynamics. If confirmed, the observation of a quantum spin ice
ground state would constitute a concrete example of a three-dimensional quantum
spin liquid - a topical state of matter which has so far mostly been explored
in lower dimensionalities.Comment: 15 pages, 3 figure
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