63 research outputs found
Evolution of superconductivity by oxygen annealing in FeTe0.8S0.2
Oxygen annealing dramatically improved the superconducting properties of
solid-state-reacted FeTe0.8S0.2, which showed only a broad onset of
superconducting transition just after the synthesis. The zero resistivity
appeared and reached 8.5 K by the oxygen annealing at 200\degree C. The
superconducting volume fraction was also enhanced from 0 to almost 100%. The
lattice constants were compressed by the oxygen annealing, indicating that the
evolution of bulk superconductivity in FeTe0.8S0.2 was correlated to the
shrinkage of lattice.Comment: 13 pages, 6 figure
Spin Configuration and Scattering Rates on the Heavily Electron-doped Surface of Topological Insulator BiSe
Heavily electron-doped surfaces of BiSe have been studied by spin and
angle resolved photoemission spectroscopy. Upon doping, electrons occupy a
series of {\bf k}-split pairs of states above the topological surface state.
The {\bf k}-splitting originates from the large spin-orbit coupling and results
in a Rashba-type behavior, unequivocally demonstrated here via the spin
analysis. The spin helicities of the lowest laying Rashba doublet and the
adjacent topological surface state alternate in a left-right-left sequence.
This spin configuration sets constraints to inter-band scattering channels
opened by electron doping. A detailed analysis of the scattering rates suggests
that intra-band scattering dominates with the largest effect coming from
warping of the Fermi surface
Spin-Resolved Photoemission on Anti-Ferromagnets: Direct Observation of Zhang-Rice Singlets in CuO
We demonstrate that it is possible to obtain spin-resolved valence band spectra with a very high
degree of spin polarization from antiferromagnetic transition metal materials if the excitation light is
circularly polarized and has an energy close to the cation 2p3/2 (L3) white line. We are able to unravel
the different spin states in the single-particle excitation spectrum of CuO and show that the top of the
valence band is of pure singlet character, which provides strong support for the existence and stability
of Zhang-Rice singlets in high-Tc superconductors
Local Electronic and Magnetic Structure of Ni below and above TC: A Spin-Resolved Circularly Polarized Resonant Photoemission Study
We report the measurement of the local Ni 3d spin polarization, not only below but also above the
Curie temperature (TC), using the newly developed spin-resolved circularly polarized 2p (L3) resonant
photoemission technique. The experiment identifies the presence of 3d8 singlets at high energies and
3d8 triplets at low energies extending all the way to the Fermi energy, both below and above TC,
showing that it is the orbital degeneracy of the 3d band and the Hund's rule splitting which is of utmost
importance to understand Ni and other 3d ferromagnets
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An analysis of the x-ray linear dichroism spectrum for NiO thin films grown on vicinal Ag(001)
Antiferromagnetic (AFM) NiO thin films are grown epitaxially on vicinal Ag(118) substrate and investigated by x-ray linear dichroism (XLD). We find that the NiO AFM spin exhibits an in-plane spin reorientation transition from parallel to perpendicular to the step edges with increasing the NiO film thickness. In addition to the conventional L{sub 2} adsorption edge, x-ray linear dichroism (XLD) effect at the Ni L{sub 3} adsorption edge is also measured and analyzed. The result identifies a small energy shift of the L{sub 3} peak. Temperature-dependent measurement confirms that the observed XLD effect in this system at the normal incidence of the x-rays originates entirely from the NiO magnetic ordering
A Spin-Resolved Photoemission Study of Photohole Lifetimes in Ferromagnetic Gadolinium
High resolution spin-resolved photoemission is used to probe the properties
of a Gd(0001) surface state. The state shows both a spin-mixing behavior
reflecting the exchange of magnons with the local moments and a reduction of
the exchange splitting with increasing temperature. The surface state
polarization at low T suggests that the surface layer has an enhanced Tc of
365K or greater. Measurements of the photoemission linewidths show that at low
temperatures, the lifetime of a majority spin photohole is predominantly
limited by electron-phonon scattering and that of a minority spin photohole by
electron-magnon scattering. Since similar behavior may be expected for bulk
states close to the Fermi level, the transport properties of this material will
also be determined by different decay mechanisms in the two channels
Combined cytogenetic and molecular methods for taxonomic verification and description of Brassica populations deriving from different origins
Agriculture faces great challenges to overcome global warming and improve system sustainability, requiring access
to novel genetic diversity. So far, wild populations and local landraces remain poorly explored. This is notably the case for
the two diploid species, Brassica oleracea L. (CC, 2n=2x=18) and B. rapa L. (AA, 2n=2x=20). In order to explore the
genetic diversity in both species, we have collected populations in their centre of origin, the Mediterranean basin, on a
large contrasting climatic and soil gradient from northern Europe to southern sub-Saharan regions. In these areas, we also
collected 14 populations belonging to five B. oleracea closely related species. Our objective was to ensure the absence of
species misidentification at the seedling stage among the populations collected and to describe thereafter their origins. We
combined flow cytometry, sequencing of a species-specific chloroplast genomic region, as well as cytogenetic analyses in
case of unexpected results for taxonomic verification. Out of the 112 B. oleracea and 154 B. rapa populations collected, 103
and 146, respectively, presented a good germination rate and eighteen populations were misidentified. The most frequent
mistake was the confusion of these diploid species with B. napus. Additionally for B. rapa, two autotetraploid populations
were observed. Habitats of the collected and confirmed wild populations and landraces are described in this study. The unique
plant material described here will serve to investigate the genomic regions involved in adaptation to climate and microbiota
within the framework of the H2020 Prima project ‘BrasExplor’
Extrinsic Magnetotransport Phenomena in Ferromagnetic Oxides
This review is focused on extrinsic magnetotransport effects in ferromagnetic
oxides. It consists of two parts; the second part is devoted to an overview of
experimental data and theoretical models for extrinsic magnetotransport
phenomena. Here a critical discussion of domain-wall scattering is given.
Results on surfacial and interfacial magnetism in oxides are presented.
Spin-polarized tunnelling in ferromagnetic junctions is reviewed and
grain-boundary magnetoresistance is interpreted within a model of
spin-polarized tunnelling through natural oxide barriers. The situation in
ferromagnetic oxides is compared with data and models for conventional
ferromagnets. The first part of the review summarizes basic material
properties, especially data on the spin-polarization and evidence for
half-metallicity. Furthermore, intrinsic conduction mechanisms are discussed.
An outlook on the further development of oxide spin-electronics concludes this
review.Comment: 133 pages, 47 figures, submitted to Rep. Prog. Phy
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