Layered kagome-lattice 3d transition metals are emerging as an exciting platform to explore the frustrated lattice geometry and quantum topology. However, the typical kagome electronic bands, ...characterized by sets of the Dirac-like band capped by a phase-destructive flat band, have not been clearly observed, and their orbital physics are even less well investigated. Here, we present close-to-textbook kagome bands with orbital differentiation physics in CoSn, which can be well described by a minimal tight-binding model with single-orbital hopping in Co kagome lattice. The capping flat bands with bandwidth less than 0.2 eV run through the whole Brillouin zone, especially the bandwidth of the flat band of out-of-plane orbitals is less than 0.02 eV along Γ-M. The energy gap induced by spin-orbit interaction at the Dirac cone of out-of-plane orbitals is much smaller than that of in-plane orbitals, suggesting orbital-selective character of the Dirac fermions.
A metal‐free 2+2 cycloaddition and 1,4‐addition sequence induced by S‐centered radicals has been achieved by treating benzene‐linked allene‐ynes with aryldiazonium tetrafluoroborates and ...DABCO‐bis(sulfur dioxide) in a one‐pot procedure. The reaction provides a greener and more practical access to functionalized cyclobutaanaphthalen‐4‐ols with valuable applications. More than 50 examples are demonstrated with excellent diastereoselectivity and chemical yields. The reaction pathway is proposed to proceed by the following steps:2+2 cycloaddition, insertion of SO2, 1,4‐addition, diazotization, and tautomerization.
Just a DAB: A new metal‐free 2+2 cycloaddition/S‐centered radical induced 1,4‐addition sequence of benzene‐linked allene‐ynes has been established by treatment with aryldiazonium tetrafluoroborates and DABCO‐bis(sulfur dioxide) under convenient reaction conditions, thus providing practical access to functionalized cyclobutaanaphthalen‐4‐ols of chemical and biomedical importance. DABCO=1,4‐diazabicyclo2.2.2octane.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Intertwining quantum order and non-trivial topology is at the frontier of condensed matter physics1–4. A charge-density-wave-like order with orbital currents has been proposed for achieving the ...quantum anomalous Hall effect5,6 in topological materials and for the hidden phase in cuprate high-temperature superconductors7,8. However, the experimental realization of such an order is challenging. Here we use high-resolution scanning tunnelling microscopy to discover an unconventional chiral charge order in a kagome material, KV3Sb5, with both a topological band structure and a superconducting ground state. Through both topography and spectroscopic imaging, we observe a robust 2 × 2 superlattice. Spectroscopically, an energy gap opens at the Fermi level, across which the 2 × 2 charge modulation exhibits an intensity reversal in real space, signalling charge ordering. At the impurity-pinning-free region, the strength of intrinsic charge modulations further exhibits chiral anisotropy with unusual magnetic field response. Theoretical analysis of our experiments suggests a tantalizing unconventional chiral charge density wave in the frustrated kagome lattice, which can not only lead to a large anomalous Hall effect with orbital magnetism, but also be a precursor of unconventional superconductivity.An unconventional chiral charge order is observed in a kagome superconductor by scanning tunnelling microscopy. This charge order has unusual magnetic tunability and intertwines with electronic topology.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
The quantum-level interplay between geometry, topology and correlation is at the forefront of fundamental physics1-15. Kagome magnets are predicted to support intrinsic Chern quantum phases owing to ...their unusual lattice geometry and breaking of time-reversal symmetry14,15. However, quantum materials hosting ideal spinorbit-coupled kagome lattices with strong out-of-plane magnetization are lacking16-21. Here, using scanning tunnelling microscopy, we identify a new topological kagome magnet, TbMn6Sn6, that is close to satisfying these criteria. We visualize its effectively defect-free, purely manganese-based ferromagnetic kagome lattice with atomic resolution. Remarkably, its electronic state shows distinct Landau quantization on application of a magnetic field, and the quantized Landau fan structure features spin-polarized Dirac dispersion with a large Chern gap. We further demonstrate the bulk-boundary correspondence between the Chern gap and the topological edge state, as well as the Berry curvature field correspondence of Chern gapped Dirac fermions. Our results point to the realization of a quantum-limit Chern phase in TbMn6Sn6, and may enable the observation of topological quantum phenomena in the RMn6Sn6 (where R is a rare earth element) family with a variety of magnetic structures. Our visualization ofthe magnetic bulk-boundary-Berry correspondence covering real space and momentum space demonstrates a proof-of-principle method for revealing topological magnets.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Electronic systems with flat bands are predicted to be a fertile ground for hosting emergent phenomena including unconventional magnetism and superconductivity1–15, but materials that manifest this ...feature are rare. Here, we use scanning tunnelling microscopy to elucidate the atomically resolved electronic states and their magnetic response in the kagome magnet Co3Sn2S2 (refs. 16–20). We observe a pronounced peak at the Fermi level, which we identify as arising from the kinetically frustrated kagome flat band. On increasing the magnetic field up to ±8 T, this state exhibits an anomalous magnetization-polarized many-body Zeeman shift, dominated by an orbital moment that is opposite to the field direction. Such negative magnetism is induced by spin–orbit-coupling quantum phase effects21–25 tied to non-trivial flat band systems. We image the flat band peak, resolve the associated negative magnetism and provide its connection to the Berry curvature field, showing that Co3Sn2S2 is a rare example of a kagome magnet where the low-energy physics can be dominated by the spin–orbit-coupled flat band.The authors show that a magnetic material with kagome lattice planes hosts a flat band near the Fermi level. Electrons in this band exhibit ‘negative magnetism’ due to the Berry curvature.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Owing to the unusual geometry of kagome lattices-lattices made of corner-sharing triangles-their electrons are useful for studying the physics of frustrated, correlated and topological quantum ...electronic states
. In the presence of strong spin-orbit coupling, the magnetic and electronic structures of kagome lattices are further entangled, which can lead to hitherto unknown spin-orbit phenomena. Here we use a combination of vector-magnetic-field capability and scanning tunnelling microscopy to elucidate the spin-orbit nature of the kagome ferromagnet Fe
Sn
and explore the associated exotic correlated phenomena. We discover that a many-body electronic state from the kagome lattice couples strongly to the vector field with three-dimensional anisotropy, exhibiting a magnetization-driven giant nematic (two-fold-symmetric) energy shift. Probing the fermionic quasi-particle interference reveals consistent spontaneous nematicity-a clear indication of electron correlation-and vector magnetization is capable of altering this state, thus controlling the many-body electronic symmetry. These spin-driven giant electronic responses go well beyond Zeeman physics and point to the realization of an underlying correlated magnetic topological phase. The tunability of this kagome magnet reveals a strong interplay between an externally applied field, electronic excitations and nematicity, providing new ways of controlling spin-orbit properties and exploring emergent phenomena in topological or quantum materials
.
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KISLJ, NUK, SBMB, UL, UM, UPUK
New chiral targets of orientational chirality have been designed and asymmetrically synthesized by taking advantage of N‐sulfinyl imine‐directed nucleophilic addition/oxidation, Suzuki‐Miyaura, and ...Sonogashira cross‐coupling reactions. Orientation of single isomers has been selectively controlled by using aryl/alkynyl levers C(sp2)‐C(sp) axis and tBuSO2‐ protecting group on nitrogen as proven by X‐ray diffraction analysis. The key structural characteristic of resulting orientational products is shown by remote through‐space blocking manner. Seventeen examples of multi‐step synthesis were obtained with modest to good chemical yields and complete orientational selectivity.
We report herein the design of the asymmetric synthesis of orientational atropisomers via Sonogashira coupling as the key step. This new category of orientational atropisomers is anticipated to have a broad impact on chemical, biomedical, and material sciences in the future.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The precise synthesis of miktoarm star polymers (MSPs) remains one of the great challenges in synthetic chemistry due to the difficulty in locating appropriate structural templates and polymer ...grafting/growing strategies with high selectivity and efficiency. Herein, ≈2 nm metal‐organic polyhedra (MOPs), constructed from the coordination of isophthalic acid (IPA) and Cu2+, are applied as templates for the precise synthesis of 24‐arm MSPs for their unique logarithmic ligand‐exchange dynamics. Six different polymers are prepared with IPA as an end group and they further coordinated with Cu2+ to afford the corresponding 24‐arm star homo‐polymers. MSPs can be obtained by mixing targeted homo‐arm star polymers in solutions upon thermal annealing. The compositions of MSPs can be facilely and precisely tuned by the recipe of the star polymer mixtures used. Interestingly, the obtained MSPs can be sorted into homo‐arm star polymers through a typical solvent extraction procedure. The hybridization and sorting process can be reversibly conducted through the cycle of thermal annealing and solvent treatment. The complex coordination framework not only opens new avenues for the facile and precise synthesis of MSPs and MOPs with hybrid functionalities, but also provides the capability to design sustainable polymer systems.
Metal‐organic polyhedra possess logarithmic ligand‐exchange dynamics that can only be activated at high temperatures. They have been applied as crosslinker templates for the synthesis of miktoarm star polymers with target compositions by thermal annealing of the mixture of star homo‐polymers. The reversible sorting process can be conducted through a typical solvent extraction procedure.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
To realize the molecular design of new functional silver(I) clusters, a new synthetic approach has been proposed, by which the weakly coordinating ligands NO3 – in a Ag20 thiolate cluster precursor ...can be substituted by carboxylic ligands while keeping its inner core intact. By rational design, novel atom-precise carboxylic or amino acid protected 20-core Ag(I)-thiolate clusters have been demonstrated for the first time. The fluorescence and electrochemical activity of the postmodified Ag20 clusters can be modulated by alrestatin or ferrocenecarboxylic acid substitution. More strikingly, when chiral amino acids were used as postmodified ligands, CD-activity was observed for the Ag20 clusters, unveiling an efficient way to obtain atom-precise chiral silver(I) clusters.
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IJS, KILJ, NUK, PNG, UL, UM
Elective single embryo transfer (eSET) has been increasingly advocated, but concerns about the lower pregnancy rate after reducing the number of embryos transferred have encouraged transfer of ...multiple embryos. Extended embryo culture combined with electively freezing all embryos and undertaking a deferred frozen embryo transfer might increase pregnancy rate after eSET. We aimed to establish whether elective frozen single blastocyst transfer improved singleton livebirth rate compared with fresh single blastocyst transfer.
This multicentre, non-blinded, randomised controlled trial was undertaken in 21 academic fertility centres in China. 1650 women with regular menstrual cycles undergoing their first cycle of in-vitro fertilisation were enrolled from Aug 1, 2016, to June 3, 2017. Eligible women were randomly assigned to either fresh or frozen single blastocyst transfer. The randomisation sequence was computer generated, with block sizes of two, four, or six, stratified by study site. For those assigned to frozen blastocyst transfer, all blastocysts were cryopreserved and a delayed frozen-thawed single blastocyst transfer was done. The primary outcome was singleton livebirth rate. Analysis was by intention to treat. This trial is registered at the Chinese Clinical Trial Registry, number ChiCTR-IOR-14005405.
825 women were assigned to each group and included in analyses. Frozen single blastocyst transfer resulted in higher rates of singleton livebirth than did fresh single blastocyst transfer (416 50% vs 329 40%; relative risk RR 1·26, 95% CI 1·14–1·41, p<0·0001). The risks of moderate or severe ovarian hyperstimulation syndrome (four of 825 0·5% in frozen single blastocyst transfer vs nine of 825 1·1% in fresh single blastocyst transfer; p=0·16), pregnancy loss (134 of 583 23·0% vs 124 of 481 25·8%; p=0·29), other obstetric complications, and neonatal morbidity were similar between the two groups. Frozen single blastocyst transfer was associated with a higher risk of pre-eclampsia (16 of 512 3·1% vs four of 401 1·0%; RR 3·13, 95% CI 1·06–9·30, p=0·029).
Frozen single blastocyst transfer resulted in a higher singleton livebirth rate than did fresh single blastocyst transfer in ovulatory women with good prognosis. The increased risk of pre-eclampsia after frozen blastocyst transfer warrants further studies.
The National Key Research and Development Program of China.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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