22 research outputs found
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
Temperature dependence of the paramagnetic spin excitations in BaFe2As2
We use inelastic neutron scattering to study temperature dependence of the
paramagnetic spin excitations in iron pnictide BaFeAs throughout the
Brillouin zone. In contrast to a conventional local moment Heisenberg system,
where paramagnetic spin excitations are expected to have a Lorentzian function
centered at zero energy transfer, the high-energy ( meV)
paramagnetic spin excitations in BaFeAs exhibit spin-wave-like features
up to at least 290 K (). Furthermore, we find that the sizes of the
fluctuating magnetic moments per Fe are essentially
temperature independent from the AF ordered state at to ,
which differs considerably from the temperature dependent fluctuating moment
observed in the iron chalcogenide FeTe [I. A. Zaliznyak {\it et al.},
Phys. Rev. Lett. {\bf 107}, 216403 (2011).]. These results suggest
unconventional magnetism and strong electron correlation effects in
BaFeAs.Comment: 5 pages, 5 figure
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Low-energy phonons and superconductivity in Sn0.8In0.2Te
We present neutron scattering measurements on low-energy phonons from a superconducting (Tc=2.7K) Sn0.8In0.2Te single-crystal sample. The longitudinal acoustic phonon mode and one transverse acoustic branch have been mapped out around the (002) Bragg peak for temperatures of 1.7 and 4.2 K. We observe a substantial energy width of the transverse phonons at energies comparable to twice the superconducting gap; however, there is no change in this width between the superconducting and normal states, and the precise origin of this energy width anomaly is not entirely clear. We also confirm that the compound is well ordered, with no indications of structural instability
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Low-energy phonons and superconductivity in Sn0.8In0.2Te
We present neutron scattering measurements on low-energy phonons from a superconducting (Tc=2.7K) Sn0.8In0.2Te single-crystal sample. The longitudinal acoustic phonon mode and one transverse acoustic branch have been mapped out around the (002) Bragg peak for temperatures of 1.7 and 4.2 K. We observe a substantial energy width of the transverse phonons at energies comparable to twice the superconducting gap; however, there is no change in this width between the superconducting and normal states, and the precise origin of this energy width anomaly is not entirely clear. We also confirm that the compound is well ordered, with no indications of structural instability
Frustrated Magnetic Interactions and Quenched Spin Fluctuations in CrAs (vol 39, 127501, 2022)
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Spin waves and spatially anisotropic exchange interactions in the S=2 stripe antiferromagnet Rb0.8Fe1.5 S2
An inelastic neutron scattering study of the spin waves corresponding to the stripe antiferromagnetic order in insulating Rb0.8Fe1.5S2 throughout the Brillouin zone is reported. The spin wave spectra are well described by a Heisenberg Hamiltonian with anisotropic in-plane exchange interactions. Integrating the ordered moment and the spin fluctuations results in a total moment squared of 27.6±4.2μB2/Fe, consistent with S≈2. Unlike XFe2As2 (X=Ca, Sr, and Ba), where the itinerant electrons have a significant contribution, our data suggest that this stripe antiferromagnetically ordered phase in Rb0.8Fe1.5S2 is a Mott-like insulator with fully localized 3d electrons and a high-spin ground state configuration. Nevertheless, the anisotropic exchange couplings appear to be universal in the stripe phase of Fe pnictides and chalcogenides
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