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This corrects the article DOI: 10.1103/PhysRevLett.127.176401.
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Multifold degenerate fermions have attracted a lot of research interest in condensed matter physics and materials science, but always lack in two dimensions. In this Letter, from symmetry analysis and lattice model construction, we demonstrate that eightfold degenerate fermions can be realized in two-dimensional systems. In nonmagnetic materials with negligible spin-orbit coupling, the gray magnetic space groups together with SU(2) spin rotation symmetry can protect the two-dimensional eightfold degenerate fermions on a certain high-symmetry axis in the Brillouin zone, no matter whether the system is centrosymmetric or noncentrosymmetric. In antiferromagnetic materials, the eightfold degenerate fermions can also be protected by certain "spin space groups." Furthermore, by first-principles electronic structure calculations, we predict that the paramagnetic phase of the monolayer LaB_{8} on a suitable substrate is a two-dimensional eightfold degenerate as well as Dirac node-line semimetal. Especially, the eightfold degenerate points are close to the Fermi level, which makes monolayer LaB_{8} a good platform to study the exotic physical properties of two-dimensional eightfold degenerate fermions.
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The quantum limit is quite easy to achieve once the band crossing exists exactly at the Fermi level (EF) in topological semimetals. In multilayered Dirac fermion systems, the density of Dirac fermions on the zeroth Landau levels (LLs) increases in proportion to the magnetic field, resulting in intriguing angle- and field-dependent interlayer tunneling conductivity near the quantum limit. BaGa2 is an example of a multilayered Dirac semimetal with its quasi-2D Dirac cone located at EF, providing a good platform to study its interlayer transport properties. In this paper, we report the negative interlayer magnetoresistance induced by the tunneling of Dirac fermions between the zeroth LLs of neighboring Ga layers in BaGa2. When the field deviates from the c-axis, the interlayer resistivity ρzz(θ) increases and finally results in a peak with the applied field perpendicular to the c-axis. These unusual interlayer transport properties are observed together in the Dirac semimetal under ambient pressure and are well explained by the model of tunneling between Dirac fermions in the quantum limit.
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Coumarin is an important class of natural organic compounds, which widely exists in a variety of plants and microorganisms. Coumarins have many biological activities and wide clinical applications, such as anti-tumor, anti-HIV, anti-bacterial, anti-inflammatory, anti-oxidation, anti-coagulation, but they have obvious toxic effects in rodents. It was found that the toxicity of coumarins in different animals and organs was significantly different, and high dose oral administration was more likely to produce toxic reactions. Based on the research and analysis of domestic and foreign literatures in recent 60 years, this paper mainly summarized the hepatotoxicity and pulmonary toxicity induced by coumarins, and probed into their possible mechanisms. It was found that the toxicity of coumarins had metabolic differences and species differences. The liver of rats and lungs of mice were more susceptible to coumarins. Toxic reactions occurred mainly in the second metabolic pathway of coumarin metabolism in vivo. In order to put forward safety considerations and evaluate the impact of coumarin on human body, it was found that coumarin is unlikely to produce hepatotoxicity at normal exposure level. It was also suggested that species differences due to different metabolic patterns in model animals should be carefully considered when assessing coumarin toxicity, in order to provide reference for clinical research and rational use of coumarins and improve the rational use of coumarins.
