The kagome lattice based on 3d transition metals is a versatile platform for novel topological phases hosting symmetry-protected electronic excitations and exotic magnetic ground states. However, the paradigmatic states of the idealized two-dimensional (2D) kagome lattice -Dirac fermions and topological flat bands -have not been simultaneously observed, partly owing to the complex stacking structure of the kagome compounds studied to date. Here, we take the approach of examining FeSn, an antiferromagnetic single-layer kagome metal with spatially-decoupled kagome planes. Using polarization-and termination-dependent angleresolved photoemission spectroscopy (ARPES), we detect the momentum-space signatures of coexisting flat bands and Dirac fermions in the vicinity of the Fermi energy. Intriguingly, when complemented with bulk-sensitive de Haas-van Alphen (dHvA) measurements, our data reveal an even richer electronic structure that exhibits robust surface Dirac fermions on specific crystalline terminations. Through band structure calculations and matrix element simulations, we demonstrate that the bulk Dirac bands arise from in-plane localized Fe-3d orbitals under kagome symmetry, while the surface state realizes a rare example of fully spin-polarized 2D Dirac fermions when combined with spin-layer locking in FeSn. These results highlight FeSn as a prototypical host for the emergent excitations of the kagome lattice. The prospect to harness these excitations for novel topological phases and spintronic devices is a frontier of great promise at the confluence of topology, magnetism, and strongly-correlated electron physics.

Double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6 have been synthesized under high-pressure and high-temperature conditions (6 GPa and 1500 °C). Their crystal structures and magnetic properties were studied by a synchrotron X-ray diffraction experiment and by magnetic susceptibility, specific heat, isothermal magnetization, and electrical resistivity measurements. Ca2MgOsO6 and Sr2MgOsO6 crystallized in monoclinic (P21/n) and tetragonal (I4/m) double-perovskite structures, respectively; the degree of order of the Os and Mg arrangement was 96% or higher. Although Ca2MgOsO6 and Sr2MgOsO6 are isoelectric, a magnetic-glass transition was observed for Ca2MgOsO6 at 19 K, while Sr2MgOsO6 showed an antiferromagnetic transition at 110 K. The antiferromagnetic-transition temperature is the highest in the family. A first-principles density functional approach revealed that Ca2MgOsO6 and Sr2MgOsO6 are likely to be antiferromagnetic Mott insulators in which the band gaps open, with Coulomb correlations of ∼1.8-3.0 eV. These compounds offer a better opportunity for the clarification of the basis of 5d magnetic sublattices, with regard to the possible use of perovskite-related oxides in multifunctional devices. The double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6 are likely to be Mott insulators with a magnetic-glass (MG) transition at ∼19 K and an antiferromagnetic (AFM) transition at ∼110 K, respectively. This AFM transition temperature is the highest among double-perovskite oxides containing single magnetic sublattices. Thus, these compounds offer valuable opportunities for studying the magnetic nature of 5d perovskite-related oxides, with regard to their possible use in multifunctional devices.

We report a comprehensive experimental investigation on the magnetic anisotropy in bulk single crystals of Cr2Ge2Te6, a quasi-two-dimensional ferromagnet belonging to the family of magnetic layered transition metal trichalcogenides that have attracted recently a big deal of interest with regard to the fundamental and applied aspects of two-dimensional magnetism. For this purpose electron spin resonance (ESR) and ferromagnetic resonance (FMR) measurements have been carried out over a wide frequency and temperature range. A gradual change in the angular dependence of the ESR linewidth at temperatures above the ferromagnetic transition temperature Tc reveals the development of two-dimensional spin correlations in the vicinity of Tc thereby proving the intrinsically low-dimensional character of spin dynamics in Cr2Ge2Te6. Angular and frequency dependent measurements in the ferromagnetic phase clearly show an easy-axis type anisotropy of this compound. Furthermore, these experiments are compared with simulations based on a phenomenological approach, which takes into account results of static magnetization measurements as well as high temperature g factors obtained from ESR spectroscopy in the paramagnetic phase. As a result the determined magnetocrystalline anisotropy energy density (MAE) KU is (0.48 ± 0.02) × 10 6 erg/cm 3 . This analysis is complemented by density functional calculations which yield the experimental MAE value for a particular value of the electronic correlation strength U . The analysis of the electronic structure reveals that the low-lying conduction band carries almost completely spin-polarized, quasihomogeneous, two-dimensional states. arXiv:1810.02560v3 [cond-mat.str-el]

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As they do not rely on the presence of any crystal symmetry, Weyl nodes are robust topological features of an electronic structure that can occur at any momentum and energy. Acting as sinks and sources of Berry curvature, Weyl nodes have been predicted to strongly affect the transverse electronic response, like in the anomalous Hall or Nernst effects. However, to observe large anomalous effects the Weyl nodes need to be close to or at the Fermi-level, which implies the band structure must be tuned by an external parameter, e.g. chemical doping or pressure. Here we show that in a ferromagnetic metal tuning of the Weyl node energy and momentum can be achieved by rotation of the magnetization. Taking Co 3 Sn 2 S 2 as an example, we use electronic structure calculations based on density-functional theory to show that not only new Weyl fermions can be created by canting the magnetization away from the easy axis, but also that the Weyl nodes can be driven exactly to the Fermi surface. We also show that the dynamics in energy and momentum of the Weyl nodes strongly affect the calculated anomalous Hall and Nernst conductivities.Materials hosting unconventional quasiparticles, such as Weyl semimetals, constitute a framework with potential for novel electronic devices. One of the grounds for such expectation is the possibility of enhancing the response to external fields by taking advantage of the topological properties of the electronic states. For a material to specifically host Weyl fermions the spin degeneracy of the electronic bands has to be removed by breaking either inversion or time-reversal symmetry (Θ). Karplus and Luttinger [1] first noticed that in a Θ-broken system the spin-orbit coupling can introduce in the manifold of Bloch states a left-right asymmetry which in turn, in the presence of an electric field, causes a Hall current at zero magnetic field. This scattering-independent mechanism originates in the so-called anomalous velocity of the wave-packets, which can be written in terms of the Berry curvature of the Bloch states in momentum space. Weyl nodes are monopoles of Berry curvature which implies first, that they can only be created and annihilated in pairs of opposite monopole charge and second, that wave-packets made out of Weyl fermions can have a large anomalous velocity. As this velocity is perpendicular to the electric field, Weyl systems can exhibit enhanced transverse electronic responses, as in the Hall or Nernst effects.This effect has been argued to be at work in different materials in which the anomalous velocity contribution intrinsic to the band-structure is at the heart of enhanced electric and thermoelectric performance both in the regime of linear [2][3][4][5][6][7] as well as in nonlinear response [8,9]. Still, a central problem for optimizing Berry-curvature-based effects is the energy of the Weyl fermions which currently is not a controlled variable from a material design point of view. Indeed, as the only symmetry restriction is to break inversion or Θ, Weyl nodes can occur at any...

The kagome lattice has long been regarded as a theoretical framework that connects lattice geometry to unusual singularities in electronic structure. Transition metal kagome compounds have been recently identified as a promising material platform to investigate the long-sought electronic flat band. Here we report the signature of a two-dimensional flat band at the surface of antiferromagnetic kagome metal FeSn by means of planar tunneling spectroscopy. Employing a Schottky heterointerface of FeSn and an n-type semiconductor Nb-doped SrTiO3, we observe an anomalous enhancement in tunneling conductance within a finite energy range of FeSn. Our first-principles calculations show this is consistent with a spin-polarized flat band localized at the ferromagnetic kagome layer at the Schottky interface. The spectroscopic capability to characterize the electronic structure of a kagome compound at a thin film heterointerface will provide a unique opportunity to probe flat band induced phenomena in an energy-resolved fashion with simultaneous electrical tuning of its properties. Furthermore, the exotic surface state discussed herein is expected to manifest as peculiar spin-orbit torque signals in heterostructure-based spintronic devices.

The ferromagnetic semiconductor Ba2NiOsO6 (Tmag ~100 K) was synthesized at 6 GPa and 1500 C. It crystallizes into a double perovskite structure a = 8.0428 plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te (Tmag < 180 K), the spin-gapless semiconductor Mn2CoAl (Tmag ~720 K), and the ferromagnetic insulators EuO (Tmag ~70 K) and Bi3Cr3O11 (Tmag ~220 K). It is also qualitatively different from known ferrimagnetic insulator/semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of Ba2NiOsO6 should increase interest in the platinum group oxides, because this new class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.3

ObjectiveTo assess the prevalence of microalbuminuria and kidney dysfunction in low-income countries and in the USA.DesignCross-sectional study of screening programmes in five countries.SettingScreening programmes in Nepal, Bolivia, the USA (National Health and Nutrition Examination Survey (NHANES) 2005–2008) Bangladesh and Georgia.ParticipantsGeneral population in Nepal (n=20 811), Bolivia (n=3436) and in the USA (n=4299) and high-risk subjects in Bangladesh (n=1518) and Georgia (n=1549).Primary and secondary outcome measuresEstimated glomerular filtration rate (eGFR)<60ml/min/1.73 m2 and microalbuminuria (defined as urinary albumin creatinine ratio values of 30–300 mg/g) were the main outcome measures. The cardiovascular (CV) risk was also evaluated on the basis of demographic, clinical and blood data.ResultsThe prevalence of eGFR<60ml/min/1.73 m2 was 19%, 3.2% and 7% in Nepal, Bolivia and the USA, respectively. In Nepal, 7% of subjects were microalbuminuric compared to 8.6% in the USA. The prevalence of participants with predicted 10-year CV disease (CVD) risk ≥10% was 16.9%, 9.4% and 17% in Nepal, Bolivia and in the USA, respectively. In Bangladesh and Georgia, subjects with eGFR<60 ml/min/1.73 m2 were 8.6% and 4.9%, whereas those with microalbuminuria were 45.4% and 56.5%, respectively. Predicted 10-year CVD risk ≥10% was 25.4% and 25% in Bangladesh and Georgia, respectively.ConclusionsRenal abnormalities are common among low-income countries and in the USA. Prevention programmes, particularly focused on those with renal abnormalities, should be established worldwide to prevent CVD and progression to end-stage renal disease.