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The Weyl semimetal (WSM), which hosts pairs of Weyl points and accompanying Berry curvature in momentum space near Fermi level, is expected to exhibit novel electromagnetic phenomena. Although the large optical/electronic responses such as nonlinear optical effects and intrinsic anomalous Hall effect (AHE) have recently been demonstrated indeed, the conclusive evidence for their topological origins has remained elusive. Here, we report the gigantic magneto-optical (MO) response arising from the topological electronic structure with intense Berry curvature in magnetic WSM Co3Sn2S2. The low-energy MO spectroscopy and the first-principles calculation reveal that the interband transitions on the nodal rings connected to the Weyl points show the resonance of the optical Hall conductivity and give rise to the giant intrinsic AHE in dc limit. The terahertz Faraday and infrared Kerr rotations are found to be remarkably enhanced by these resonances with topological electronic structures, demonstrating the novel low-energy optical response inherent to the magnetic WSM. The evidence of topological origin for the recently observed anomalous Hall effect remains elusive. Here, the authors report that the resonance of the optical Hall conductivity resulted from topological electronic structure gives rise to the large intrinsic anomalous Hall effect in the magnetic Weyl semimetal Co3Sn2S2. [ABSTRACT FROM AUTHOR]

Pyrochlore Tl2Mn2O7 has been found to exhibit a colossal magneto-resistance (CMR) that is comparable to that for the perovskite manganites such as La1−xSrxMnO3. In order to probe the microscopic electronic structures of Tl2Mn2O7, we have measured its optical conductivity σ(ω) in wide ranges of photon energy, temperature (T), and external magnetic field (B). We have observed very strong variations of σ(ω) with T and B near the Curie temperature, where the CMR manifests itself. Analyses on the variations in σ(ω) show that both T- and B-induced evolutions of the electronic structures in Tl2Mn2O7 are very similar to each other, and that they are universally related to the development of macroscopic magnetization. We have also observed a pronounced Kerr rotation at the plasma edge of the reflectivity. [Copyright &y& Elsevier]

In the quest for switching of the charge carrier type in conductive materials, we focus on nonsymmorphic crystals, which are expected to have highly anisotropic folded Fermi surfaces due to symmetry requirements. Following a simple tight-binding model simulation, we prepare nonsymmorphic IrO2 single-crystalline films with various growth orientations by molecular beam epitaxy, and systematically quantify their Hall effect for the corresponding field directions. The results clearly demonstrate that the dominant carrier type can be intrinsically controlled by the magnetic field direction, as also evidenced by first-principles calculations revealing nontrivial momentum dependence of the group velocity and mass tensor on the folded Fermi surfaces and its anisotropic nature for the field direction. [ABSTRACT FROM AUTHOR]

Chirality-controlled synthesis of carbon nanotubes (CNTs) is one of the ultimate goals in the field of nanotube synthesis. At present, direct synthesis achieving a purity of over 90%, which can be called single-chirality synthesis, has been achieved for only two types of chiralities: (14,4) and (12,6) CNTs. Here, we realized an ultrahigh-purity (∼95.8%) synthesis of (6,5) CNTs with a trimetallic catalyst NiSnFe. Partial formation of Ni 3 Sn crystals was found within the NiSnFe nanoparticles. The activation energy for the selective growth of (6,5) CNTs decreased owing to the formation of Ni 3 Sn crystals, resulting in the high-purity synthesis of (6,5) CNTs. Transmission electron microscopy (TEM) reveals that one-dimensional (1D) crystals of periodic strip lines with 8.8 Å spacing are formed within the as-grown ultrahigh-purity (6,5) CNTs, which are well-matched with the simulated TEM image of closely packed 37 (6,5) CNTs with 2.8 Å intertube distance, indicating the direct formation of chirality-pure (6,5)-CNT bundle structures. The photoluminescence (PL) lifetime increases more than 20 times by the formation of chirality-pure bundle structures of (6,5) CNTs compared to that of isolated (6,5) CNTs. This can be explained by exciton delocalization or intertube excitons within bundle structures of chirality-pure (6,5) CNTs.

Pressurized hydrogen-based superconductors are phonon-mediated superconductors that exhibit high phonon frequencies. In these superconductors, in addition to the density of states (DOS) at the Fermi energy ( E F ), the energy dependence of the DOS around E F becomes important for evaluating their transition temperature ( T c ). Systems with peak structures in the DOS around E F , such as I m 3 ¯ m H 3 S and F m 3 ¯ m LaH 10 , highlight this point. We use the fully ab initio Eliashberg method to investigate this phenomenon in I m 3 ¯ m CaH 6 and F m 3 ¯ m ThH 10 with a dip structure in their DOS around E F . Our calculated T c values (225-235 K for CaH 6 at 200 GPa and 156-158 K for ThH 10 at 170 GPa) are quantitatively consistent with the experimental results. Remarkably, our results from the self-consistent treatment of the electron Green's function contrasts with those cases with a peak structure in the DOS. This finding unifies the understanding of how DOS structures influence the evaluation of T c ., (© 2024. The Author(s).)

We investigate ultrafast dynamics of the anomalous Hall effect (AHE) in the topological antiferromagnet Mn_{3}Sn with sub-100 fs time resolution. Optical pulse excitations largely elevate the electron temperature up to 700 K, and terahertz probe pulses clearly resolve ultrafast suppression of the AHE before demagnetization. The result is well reproduced by microscopic calculation of the intrinsic Berry-curvature mechanism while the extrinsic contribution is clearly excluded. Our work opens a new avenue for the study of nonequilibrium AHE to identify the microscopic origin by drastic control of the electron temperature by light.

Cesium ion (Cs + ) resistance has been reported in bacteria but is poorly understood as reports on Cs + -resistant bacteria have been limited. We previously reported a novel Cs + /H + antiporter CshA implicated in Cs + -resistance in Microbacterium sp. TS-1. The present study used the same screening method to isolate novel Cs + -sensitive mutants and their revertants from TS-1. A comparative mutation site analysis using whole-genome sequencing revealed that MTS1_03028 encodes the Mg 2+ transporter MgtE and is a candidate Cs + resistance-related gene. We performed a bioinformatic analysis of MTS1_03028 and complementation experiments on Cs + resistance in the TS-1 MTS1_03028 mutants Mut5 and Mut7 as well as Escherichia coli expressing MTS1_03028 in the presence of Mg 2+ . We established the role of MgtE in Cs + resistance through a functional analysis of TS-1. Enhancing Mg 2+ transport by expression of MTS_03028 conferred increased Cs + resistance. When this strain was exposed to Cs + concentrations exceeding 200 mM, CshA consistently lowered the intracellular Cs + concentration. To our knowledge, the present study is the first to clarify the mechanism of Cs + resistance in certain bacteria. The study findings offer important insights into the mechanism of bacterial resistance to excess Cs + in the environment, suggesting the potential for bioremediation in high Cs-contaminated areas., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Ishida, Koretsune, Ishiuchi, Teshima and Ito.)

The radionuclide isotopes ( 134 Cs and 137 Cs) of Cesium (Cs), an alkali metal, are attracting attention as major causes of radioactive contamination. Although Cs + is harmful to the growth of plants and bacteria, alkaliphilic bacterium Microbacterium sp. TS-1, isolated from a jumping spider, showed growth even in the presence of 1.2 M CsCl. The maximum concentration of Cs + that microorganisms can withstand has been reported to be 700 mM till date, suggesting that the strain TS-1 is resistant to a high concentration of Cs ions. Multiple reports of cesium ion-resistant bacteria have been reported, but the detailed mechanism has not yet been elucidated. We obtained Cs ion-sensitive mutants and their revertant mutants from strain TS-1 and identified a Cs ion resistance-related gene, MTS1_00475 , by performing SNP analysis of the whole-genome sequence data. When exposed to more than 200 mM Cs + concentration, the intracellular Cs + concentration was constantly lowered by MTS1_00475, which encodes the novel low-affinity Cs + /H + antiporter. This study is the first to clarify the mechanism of cesium resistance in unexplained cesium-resistant microorganisms. By clarifying the new cesium resistance mechanism, it can be expected to be used as a bioremediation tool for treating radioactive Cs + contaminated water., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Koretsune, Ishida, Kaneda, Ishiuchi, Teshima, Marubashi, Satoh and Ito.)

Anomalous Nernst effect (ANE), converting a heat flow to transverse electric voltage, originates from the Berry phase of electronic wave function near the Fermi energy E F . Thus, the ANE provides a sensitive probe to detect a topological state that produces large Berry curvature. In addition, a magnet that exhibits a large ANE using low-cost and safe elements will be useful to develop a novel energy harvesting technology. Here, we report our observation of a high ANE exceeding 3 microvolts per kelvin above room temperature in the kagome ferromagnet Fe 3 Sn with the Curie temperature of 760 kelvin. Our theoretical analysis clarifies that a “nodal plane” produces a flat hexagonal frame with strongly enhanced Berry curvature, resulting in the large ANE. Our discovery of the large ANE in Fe 3 Sn opens the path for the previously unexplored functionality of flat degenerate electronic states and for developing flexible film thermopile and heat current sensors.

Recently found anomalous Hall, Nernst, magnetooptical Kerr, and spin Hall effects in the antiferromagnets Mn 3 X (X = Sn, Ge) are attracting much attention for spintronics and energy harvesting. Since these materials are antiferromagnets, the origin of these functionalities is expected to be different from that of conventional ferromagnets. Here, we report the observation of ferroic order of magnetic octupole in Mn 3 Sn by X-ray magnetic circular dichroism, which is only predicted theoretically so far. The observed signals are clearly decoupled with the behaviors of uniform magnetization, indicating that the present X-ray magnetic circular dichroism is not arising from the conventional magnetization. We have found that the appearance of this anomalous signal coincides with the time reversal symmetry broken cluster magnetic octupole order. Our study demonstrates that the exotic material functionalities are closely related to the multipole order, which can produce unconventional cross correlation functionalities., (© 2021. The Author(s).)

The recent discoveries of strikingly large zero-field Hall and Nernst effects in antiferromagnets Mn 3 X (X = Sn, Ge) have brought the study of magnetic topological states to the forefront of condensed matter research and technological innovation. These effects are considered fingerprints of Weyl nodes residing near the Fermi energy, promoting Mn 3 X (X = Sn, Ge) as a fascinating platform to explore the elusive magnetic Weyl fermions. In this review, we provide recent updates on the insights drawn from experimental and theoretical studies of Mn 3 X (X = Sn, Ge) by combining previous reports with our new, comprehensive set of transport measurements of high-quality Mn 3 Sn and Mn 3 Ge single crystals. In particular, we report magnetotransport signatures specific to chiral anomalies in Mn 3 Ge and planar Hall effect in Mn 3 Sn, which have not yet been found in earlier studies. The results summarized here indicate the essential role of magnetic Weyl fermions in producing the large transverse responses in the absence of magnetization.

Using the ab initio local force method, we investigate the formation mechanism of the helical spin structure in GdRu_{2}Si_{2} and Gd_{2}PdSi_{3}. We calculate the paramagnetic spin susceptibility and find that the Fermi surface nesting is not the origin of the incommensurate modulation, in contrast to the naive scenario based on the Ruderman-Kittel-Kasuya-Yosida mechanism. We then decompose the exchange interactions between the Gd spins into each orbital component, and show that spin-density-wave type interaction between the Gd-5d orbitals is ferromagnetic, but the interaction between the Gd-4f orbitals is antiferromagnetic. We conclude that the competition of these two interactions, namely, the interorbital frustration, stabilizes the finite-Q structure.