In contrast to conventional BCS superconductors, the observation that superconductivity in unconventional high-temperature materials appears in close proximity to a static antiferromagnetic phase ...suggests that magnetism plays a fundamental role in the microscopic origins of superconductivity. This review provides an overview of how elastic and inelastic neutron scattering is used to determine the magnetic structures and the doping evolution of spin excitations in iron-based superconductors. The interplay between magnetism and superconductivity is contrasted with related behavior in the copper oxide and heavy fermion superconductors and is important to future theoretical efforts. High-transition temperature (high-T sub()c superconductivity in the iron pnictides or chalcogenides emerges from the suppression of the static antiferromagnetic order in their parent compounds, similar to copper oxide superconductors. This raises a fundamental question concerning the role of magnetism in the superconductivity of these materials. Neutron scattering, a powerful probe to study the magnetic order and spin dynamics, plays an essential role in determining the relationship between magnetism and superconductivity in high-T sub()csuperconductors. The rapid development of modern neutron time-of-flight spectrometers allows a direct determination of the spin dynamical properties of iron-based superconductors throughout the entire Brillouin zone. In this paper, an overview is presented of the neutron scattering results on iron-based superconductors, focusing on the evolution of spin-excitation spectra as a function of electron and hole doping and isoelectronic substitution. Spin dynamical properties of iron-based superconductors are compared with those of copper oxide and heavy fermion superconductors and the common features of spin excitations in these three families of unconventional superconductors and their relationship with superconductivity are discussed.
High-temperature superconductivity in the iron-based materials emerges from, or sometimes coexists with, their metallic or insulating parent compound states. This is surprising, as these undoped ...states exhibit dramatically different antiferromagnetic spin arrangements and Néel temperatures. Although there is a general consensus that magnetic interactions are important for superconductivity, much remains unknown concerning the microscopic origin of the magnetic states. In this review, we summarize the progress in this area, focusing on recent experimental and theoretical results, and their microscopic implications. We conclude that the parent compounds are in a state that is more complex than that 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. PUBLICATION ABSTRACT
The design of highly efficient, stable, and noble‐metal‐free bifunctional electrocatalysts for overall water splitting is critical but challenging. Herein, a facile and controllable synthesis ...strategy for nickel–cobalt bimetal phosphide nanotubes as highly efficient electrocatalysts for overall water splitting via low‐temperature phosphorization from a bimetallic metal‐organic framework (MOF‐74) precursor is reported. By optimizing the molar ratio of Co/Ni atoms in MOF‐74, a series of CoxNiyP catalysts are synthesized, and the obtained Co4Ni1P has a rare form of nanotubes that possess similar morphology to the MOF precursor and exhibit perfect dispersal of the active sites. The nanotubes show remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic performance in an alkaline electrolyte, affording a current density of 10 mA cm−2 at overpotentials of 129 mV for HER and 245 mV for OER, respectively. An electrolyzer with Co4Ni1P nanotubes as both the cathode and anode catalyst in alkaline solutions achieves a current density of 10 mA cm−2 at a voltage of 1.59 V, which is comparable to the integrated Pt/C and RuO2 counterparts and ranks among the best of the metal‐phosphide electrocatalysts reported to date.
An unusual nanotube of nickel–cobalt bimetal phosphides is produced via a facile and controllable low‐temperature phosphorization from a bimetallic metal‐organic framework (MOF‐74) by optimizing the molar ratio of Co/Ni atoms in MOF precursor. It shows remarkable hydrogen evolution reaction and oxygen evolution reaction catalytic performance in an alkaline electrolyte and can be used as a highly efficient electrocatalyst for overall water splitting.
The separation of acetylene and carbon dioxide is an essential but challenging process owing to the similar molecular sizes and physical properties of the two gas molecules. Notably, these molecules ...usually exhibit different orientations in the pore channel. We report an adsorption site selective occupation strategy by taking advantage of differences in orientation to sieve the C2H2 from CO2 in a judiciously designed amine‐functionalized metal–organic framework, termed CPL‐1‐NH2. In this material, the incorporation of amino groups not only occupies the adsorption sites of CO2 molecules and shields the interaction of uncoordinated oxygen atom and CO2 molecules resulting in a negligible adsorption amount and a decrease in enthalpy of adsorption but also strengthened the binding affinity toward C2H2 molecules. This material thus shows an extremely high amount of C2H2 at low pressure and a remarkably high C2H2/CO2 IAST selectivity (119) at 1 bar and 298 K.
Metal–organic framework (CPL‐1‐NH2) with keyhole‐like pore apertures offers selective adsorption site properties for gas separation. Amine groups limit interactions with CO2 molecules by decreasing the enthalpy of CO2 adsorption, whereas the binding affinity of C2H2 is increased (see picture, distances in Å). CPL‐1‐NH2 demonstrates a remarkably high C2H2 selectivity with C2H2/CO2 (50/50) mixtures at 1 bar and 298 K.
Understanding the microscopic origins of electronic phases in high-transition temperature (high-Tc) superconductors is important for elucidating the mechanism of superconductivity. In the ...paramagnetic tetragonal phase of BaFe2–xTxAs2 (where T is Co or Ni) iron pnictides, an in-plane resistivity anisotropy has been observed. Here, we use inelastic neutron scattering to show that low-energy spin excitations in these materials change from fourfold symmetric to twofold symmetric at temperatures corresponding to the onset of the in-plane resistivity anisotropy. Because resistivity and spin excitation anisotropies both vanish near optimal superconductivity, we conclude that they are likely intimately connected.
In a superconductor electrons form pairs and electric transport becomes dissipation-less at low temperatures. Recently discovered iron-based superconductors have the highest superconducting ...transition temperature next to copper oxides. In this article, we review material aspects and physical properties of iron-based superconductors. We discuss the dependence of transition temperature on the crystal structure,the interplay between antiferromagnetism and superconductivity by examining neutron scatering experiments, and the electronic properties of these compounds obtained by angle-resolved photoemission spectroscopy in link with some results from scanning tunneling microscopy/spectroscopy measurements.Possible microscopic model for this class of compounds is discussed from a strong coupling point of view.
Magnetism in two-dimensional (2D) van der Waals (vdW) materials has recently emerged as one of the most promising areas in condensed matter research, with many exciting emerging properties and ...significant potential for applications ranging from topological magnonics to low-power spintronics, quantum computing, and optical communications. In the brief time after their discovery, 2D magnets have blossomed into a rich area for investigation, where fundamental concepts in magnetism are challenged by the behavior of spins that can develop at the single layer limit. However, much effort is still needed in multiple fronts before 2D magnets can be routinely used for practical implementations. In this comprehensive review, prominent authors with expertise in complementary fields of 2D magnetism (i.e., synthesis, device engineering, magneto-optics, imaging, transport, mechanics, spin excitations, and theory and simulations) have joined together to provide a genome of current knowledge and a guideline for future developments in 2D magnetic materials research.
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