Abstract
Spin-valley locking in monolayer transition metal dichalcogenides has attracted enormous interest, since it offers potential for valleytronic and optoelectronic applications. Such an exotic ...electronic state has sparsely been seen in bulk materials. Here, we report spin-valley locking in a Dirac semimetal BaMnSb
2
. This is revealed by comprehensive studies using first principles calculations, tight-binding and effective model analyses, angle-resolved photoemission spectroscopy measurements. Moreover, this material also exhibits a stacked quantum Hall effect (QHE). The spin-valley degeneracy extracted from the QHE is close to 2. This result, together with the Landau level spin splitting, further confirms the spin-valley locking picture. In the extreme quantum limit, we also observed a plateau in the
z
-axis resistance, suggestive of a two-dimensional chiral surface state present in the quantum Hall state. These findings establish BaMnSb
2
as a rare platform for exploring coupled spin and valley physics in bulk single crystals and accessing 3D interacting topological states.
This study sought to resolve whether sturgeon (Acipenseridae) sagittae (otoliths) contain a non‐vaterite fraction and to quantify how large a non‐vaterite fraction is using neutron diffraction ...analysis. This study found that all otoliths examined had a calcite fraction that ranged from 18 ± 6 to 36 ± 3% by mass. This calcite fraction is most probably due to biological variation during otolith formation rather than an artefact of polymorph transformation during preparation.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Atoms and molecules <0.9 nm in diameter can be incorporated in the cages formed by hydrogen-bonded water molecules making up the crystalline solid clathrate hydrates. For these materials ...crystallographic structures generally fall into 3 categories, which are 2 cubic forms and a hexagonal form. A unique clathrate hydrate structure, previously known only hypothetically, has been synthesized at high pressure and recovered at 77 K and ambient pressure in these experiments. These samples contain Xe as a guest atom and the details of this previously unobserved structure are described here, most notably the host-guest ratio is similar to the cubic Xe clathrate starting material. After pressure quench recovery to 1 atmosphere the structure shows considerable metastability with increasing temperature (T <160 K) before reverting back to the cubic form. This evidence of structural complexity in compositionally similar clathrate compounds indicates that the reaction path may be an important determinant of the structure, and impacts upon the structures that might be encountered in nature.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
The Wide Angle Neutron Diffractometer (WAND) at the High Flux Isotope Reactor (HFIR), Oak Ridge National Laboratory (ORNL) has been built and continues to be, a joint project between ORNL and the ...Japan Atomic Energy Agency (JAEA). Equipped with a 1-dimensional position sensitive detector (PSD), the instrument is a multi-purpose instrument for both powder and single crystal diffraction. WAND is currently in the process of a 2-phase upgrade to become a world-class, general purpose instrument. In phase 1, finished in the beginning of 2016, the whole instrument was essentially re-built from scratch, keeping only the front-end and the 1-D PSD. Phase 2 will replace the 1-D PSD with the state-of-the-art BNL120 2-D PSD which comes from the Los Alamos Neutron Science Center. Currently, the detector is integrated off-line into the data acquisition architecture at HFIR and SNS. The new instrument, WAND2, will have event mode capability, improved efficiency, and higher resolution and will be available for general users in the proposal call 2018A. This contribution presents results highlighting the improvements on WAND after phase 1. The upgraded instrument now accommodates the whole suite of available sample environment (50 mK–1500 K, magnetic fields (5 T), high pressures (4 GPa)). Also, the background could be reduced significantly by a factor of 2 through improved shielding, allowing the detection of weak signals. The phase 2 upgrade will require new electronics, data acquisition, and visualization and will result in an altogether new instrument: WAND2.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Superconductivity in the iron pnictides emerges from metallic parent compounds exhibiting intertwined stripe-type magnetic order and nematic order, with itinerant electrons suggested to be essential ...for both. Here we use x-ray and neutron scattering to show that a similar intertwined state is realized in semiconducting KFe0.8Ag1.2Te2 (K5Fe4Ag6Te10) without itinerant electrons. We find that Fe atoms in KFe0.8Ag1.2Te2 form isolated 2×2 blocks, separated by nonmagnetic Ag atoms. Long-range magnetic order sets in below TN≈35 K, with magnetic moments within the 2×2 Fe blocks ordering into the stripe-type configuration. A nematic order accompanies the magnetic transition, manifest as a structural distortion that breaks the fourfold rotational symmetry of the lattice. The nematic orders in KFe0.8Ag1.2Te2 and iron pnictide parent compounds are similar in magnitude and in how they relate to the magnetic order, indicating a common origin. Since KFe0.8Ag1.2Te2 is a semiconductor without itinerant electrons, this indicates that local-moment magnetic interactions are integral to its magnetic and nematic orders, and such interactions may play a key role in iron-based superconductivity.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
Filled skutterudite antimonides, are cubic compounds with the formula RM4Sb12, where R is a rare-earth element (such as La or Ce), and M is a transition metal (for example, Fe or Co). The rare-earth ...ion is weakly bound in an oversized atomic cage formed by the other atoms. Its presence has been shown to cause a dramatic reduction in the lattice component of the thermal conductivity, while having little effect on the electronic properties of the compound. This combination of properties makes filled skutterudites of interest as thermoelectric materials. It has been suggested that localized, incoherent vibrations of the rare-earth ion are responsible for the reduction in thermal conductivity, but no direct evidence for these local vibrational modes exists. Here we report the observation of local modes in La-filled skutterudites, using heat capacity, elastic constant and inelastic neutron scattering measurements. The La atoms show unusual thermodynamic behaviour, characterized by the presence of two low-energy localized modes. Our results suggest that consideration of local modes will play an important role in the design of the next generation of thermoelectric materials.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The skutterudite structure,
M
4
Pn
12 (cubic
Im-
3
¯
), where
M
=
Group VIII transition metal and
Pn
=
pnicogen, can be filled to varying degree by up to one atom per formula unit of a lanthanide, ...actinide, alkaline earth, alkali, or thallium atom,
A
1−
x
M
4
Pn
12. Skutterudite phases are of interest as promising thermoelectric materials. The available database of all reported crystal structure refinements of filled and unfilled skutterudites are analyzed to identify common structural responses to filling. As the filling fraction increases, the cell volume increases by about 3.6%, both the
y and
z positional parameters of the 24
g Wyckoff sites occupied by the pnicogen increase, the four-membered pnicogen ring becomes more square, and the mean-square displacement of the filling atom decreases. Details of the structural response to filling can be correlated with physical properties and used as input to build more accurate theoretical models. Crystal structure refinements of neutron powder diffraction data also are reported for three Tl-filled skutterudites, Tl
0.25Co
4Sb
12, Tl
0.51Co
4Sb
11.5Sn
0.5, and Tl
0.75Co
3FeSb
12.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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