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  • Predicted reaction energy path for AlH3 formation on Ti-doped Al(111)

    A defect-mediated direct synthesis of alane (AlH3) from its elements was predicted and verified experimentally. Alane has potential use as a hydrogen storage material with its capacity of 10.1 weight % H2 and relative ease of releasing hydrogen below 100 °C. Alane has not found broad practical use for over 70 years due to difficulties of direct synthesis from its elements. Using density functional theory researchers showed defect-mediated formation of alane monomers on crystalline faces of aluminum, namely Al(111), in a two-step process: (1) dissociative adsorption...

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  • The anisotropic upper critical field as a function of temperature for a stoichiometric single crystal.

    A member of the complex family of iron-based superconductors has been newly synthesized, shown to be highly ordered, and exhibits nearly optimal properties.  Well-ordered, single crystals of CaKFe4As4 superconductors have allowed researchers to remove one of the veils of complexity for iron-based superconductors—disorder.  Previously, our understanding of the higher transition temperatures, and promising high-magnetic field properties of iron-based superconductors has been associated with compounds with significant chemical disorder, making it hard to...

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  • Schematic representation of how the adatoms (small spheres) are guided by the electric field. The non-intercalated domain shown in the middle of the figure has higher electrostatic potential. An electric field is generated at the boundary and, in this case, the middle region attracts the adatoms.

    Researchers have shown how the motion of individual atoms on surfaces of graphene—a one atom thick layer of carbon—can be controlled. The adatom diffusion rate and hopping direction can be tuned by lowering the diffusion barrier using an effective electric field. This was shown using in situ scanning tunneling microscopy at low temperatures and the mechanism was elucidated using first-principles calculations. The electric field is locally tuned by inserting metal atoms below graphene. The metal atoms can be added to form regions of higher charge compared to areas without intercalated...

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  • The image in the center shows a sketch of topological dispersion in PtSn4. The data on the left demonstrate the presence of Dirac cones near edges of the central image. The data on the right show double Dirac dispersion that forms Dirac arc nodes visible near the center of the sketch.

    Electrons in a newly discovered metal, PtSn4, nearly reach speed of light in ways not seen in other materials. Like navigating the seas, electrons are shipped through metals and their movement is governed by the features of their own liquid, the Fermi sea. Like the sea, which can be calm to stormy, with currents and whirlpools that challenge navigation, electrons are shipped through metals governed by the varying topology of the electronic sea, which govern the electron’s speed. To date, only isolated points (Dirac points) with relatively small numbers of conduction electrons have been...

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  • Image of the Fermi surface (left) and band dispersion (right) along a red line cut. At 130 K a gapped branch appears that is due to the surface CDW

    Discovery of an unconventional charge density wave (CDW) in purple bronze, a molybdenum oxide, points to a possible new pathway to high temperature superconductivity. A CDW is a state of matter where electrons bunch together periodically, like a standing wave of light or water. CDWs and superconductivity are frenemies, since they share a common origin and often coexist, yet compete for dominance. Conventional CDWs and superconductivity arise from interactions of electrons with lattice vibrations (phonons), while electron-electron interactions are the likely origin of unconventional, high...

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  • “Ship-in-a-Bottle” synthesis for Pt nanoparticles encapsulated in SiO2 (PtX@mSiO2, X= Sn,Pb,Zn).

    X is introduced by flowing metallic salt into a “bottle”.  mSiO2 is permeable to reactants including furfural and hydrogen.

    For conversion of furfural to alcohol, PtSn yields 100% conversion (2.7x over Pt) and gives 98% selectivity (4.3x over Pt).

    A new “ship-in-a-bottle” approach to making nano-sized intermetallic compound catalysts (materials that increase how fast chemicals can be made) offers more control over stability, activity, product selectivity, and conversion efficiency than possible before.  The approach involves encapsulating the catalyst inside a “glass-bottle” made from porous silica (a.k.a. sand), and the ordered compound self-assembles, forming a designer ship in a bottle.  The development of the new synthesis approach arose by integrating experimental and computational studies to show self-assembly and...

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  • The Cu2+ spins (s=1/2 showing by the red allows) fluctuate  even at an ultra-low temperature of 0.02 K, showing a novel quantum spin liquid evidenced by NMR and uSR measurements. 

    Unlike most materials, a newly discovered oxide of lead, copper, and tellurium does not show an orderly arrangement of electron spins near the temperature of “absolute zero” Kelvin (-460 °F).  Approaching “absolute zero”, thermal vibrations slow and typically atoms, and their electron spins, find orderly arrangements resulting in long-range symmetry. In this material the electron spins fail to find an ordered state and thus are frustrated.  Their spins (called quantum spins) mimic water, which lacks any long-range order, and hence these odd materials are called quantum spin...

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  • Excited state of the solid-state emitter is shifted by random amount Δ from the desired position. The optical 180° control pulses are applied periodically, with a delay τ. In the rotating frame, each pulse swaps the ground and the excited state, reversing the detuning Δ → −Δ.

    Much like being slightly off the frequency of a radio station destroys radio reception, the quality of light-emitting technologies has, until now, been severely limited by random fluctuations in the frequency of the emitted photons.  Scientists demonstrated how this photon detuning can be suppressed using a series of short, controlled pulses applied to the emitter.  The elegant solution is robust and applicable for many quantum systems, removing a major roadblock on the way to implementing large-scale quantum networks.  The heart of these quantum-enhanced technologies is...

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  • Cover featuring an image from Petit et al. The figure shows the 3D Fermi surface for a paramagnetic compound of gadolinium and magnesium.

    Theoretical modeling has led to a key development in our understanding of the deeply complex magnetic properties in a series of rare-earth intermetallic materials.  Rare-earth elements are unique in that their cores hold strongly localized electrons that underpin their novel magnetic properties.  When combined with transition metals, rare earths become technologically-useful intermetallic materials.  Here gadolinium—an element from the middle of the rare earth series—and either magnesium, zinc, or cadmium was combined to create the materials.  Researchers developed a...

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  • Shown is the temperature dependence of the band dispersion at the hole pocket divided by the Fermi function.  Researchers found that upon increase of the temperature the electron pockets remain intact, while the hole pockets vanished above 165 K. The pink arrow points to a band located above the hole band.

    For the first time, a temperature-driven contour change in an electron behavioral map—known as the Fermi surface—has been reported.  The key properties of conducting materials are determined by the behavior of the electrons that reside on so called “Fermi surface.”  Changes in the shape of this surface, known as Lifshitz transitions, previously were seen only when substantial pressure was applied or the chemical composition of the material was modified.  Employing a technique that uses light energy (photons) to study electron properties within a sample, known as angle-...

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